Key scheduling and project planning terms used throughout this course and the broader industry. Terms are listed alphabetically.
| Term | Definition |
|---|---|
| Backward pass | The calculation that determines the latest allowable start and finish dates for each activity in a network schedule, working backwards from the project end date or a late-finish constraint. |
| Baseline schedule | The approved, time-phased project schedule used as a fixed reference point for measuring actual performance throughout the project. Changes to the baseline require formal change control. |
| Basis document | A narrative document that explains the assumptions, methods, data sources, constraints, and rationale underlying the project schedule. Also called the Basis of Schedule or Schedule Narrative. |
| Consolidated schedule | A schedule that integrates multiple contractors’ or work packages’ individual schedules into a single, unified project-level view for management oversight and interface management. |
| Contingency | Reserve time (schedule contingency) or budget allocated to account for identified project risks and inherent schedule uncertainty. Typically determined through Schedule Risk Analysis (SRA). |
| Critical activity | Any activity that lies on the critical path, meaning it has zero (or near-zero) total float and directly affects the project completion date if delayed. |
| Critical path | The longest continuous sequence of dependent activities from project start to finish. Any delay to a critical activity delays the project completion date by the same amount. |
| Dangling logic | A logic error in a schedule where an activity has no predecessor (other than the project start) or no successor (other than the project end), leaving it incompletely connected to the network. |
| Date constraint | An imposed date restriction applied to an activity that overrides the calculated early or late dates — for example, “Start No Earlier Than” (SNET) or “Finish No Later Than” (FNLT). |
| Detail activity | A work schedule activity representing a discrete, measurable unit of work at the lowest level of schedule control, typically aligned to a WBS work package. |
| Detail schedule | A schedule containing individual work activities at a level of detail sufficient to plan, execute, and control day-to-day project work. Compare with Summary schedule. |
| Deterministic critical path | The longest path through a schedule calculated using fixed, single-point duration estimates, as opposed to probabilistic (three-point) estimates used in Schedule Risk Analysis. |
| Duration | The total calendar or working-time span required to complete an activity, typically expressed in working days, hours, or weeks. Distinct from effort (work hours). |
| Finish no earlier than (FNET) | A date constraint specifying that an activity cannot finish before a specified date. It constrains the early finish but does not affect the late finish. |
| Finish no later than (FNLT) | A date constraint specifying that an activity must finish on or before a specified date. It constrains the late finish and may reduce total float. |
| Finish-to-finish (F–F) | A logical relationship where the successor activity cannot finish until the predecessor has finished. An optional lag may delay the successor’s finish further. |
| Finish-to-start (F–S) | The most common logical relationship: the successor cannot start until the predecessor has finished. The default relationship type in most scheduling software. |
| Float | The amount of scheduling flexibility available for an activity without delaying the project end date (total float) or the next activity’s start (free float). Also called slack. |
| Forward pass | The calculation that determines the earliest possible start and finish dates for each activity, working forward from the project start date or an early-start constraint. |
| Fragnet | A fragment of a schedule network representing a defined scope of work — typically a change event or delay scenario — that can be inserted into the baseline schedule for analysis. |
| Free float | The amount of time an activity can be delayed without delaying the early start of any immediately following (successor) activity. |
| Giver / Receiver | A convention describing float relationships between parallel activities. The “giver” activity holds float; the “receiver” activity on the critical path cannot use that float without impact to the giver’s completion. |
| Horizontal traceability | The ability to trace a schedule activity across levels of the schedule hierarchy — from programme-level summary to detail level — at the same point in time. |
| Integrated Master Schedule (IMS) | A comprehensive, networked schedule that integrates all programme elements, contractors, and work packages into a single performance measurement tool. Common on defence and major infrastructure programmes. |
| Intermediate Schedule | A schedule at a level of detail between the summary and detail schedules — often used for contractor milestone reporting or cross-interface coordination. |
| Lag | A positive time offset applied to a relationship that delays the start or finish of the successor activity beyond what the predecessor’s dates alone would determine. |
| Lead | A negative lag — an offset that allows the successor activity to start (or finish) before the predecessor has finished. Use leads with care as they can distort float calculations. |
| Level-of-effort (LOE) activity | A support-type activity whose duration is determined by the span of the activities it supports, rather than a discrete deliverable. Typically represents project management overhead or sustained support. |
| Longest path | The sequence of activities from project start to finish with the greatest total duration. In the absence of date constraints, the longest path equals the critical path. |
| Merge bias | A statistical phenomenon whereby the actual earliest completion date at a path convergence (merge point) is later than the deterministic schedule predicts, because any one of the converging paths may cause a delay. |
| Milestone | A significant event in the project schedule representing an achievement, contractual obligation, or key deliverable. Milestones have zero duration and are used to mark boundaries and trigger reporting. |
| Must finish on (MFON) | A hard date constraint specifying that an activity must finish on exactly the specified date. No float is permitted — the activity is constrained in both directions. |
| Must start on (MSON) | A hard date constraint specifying that an activity must start on exactly the specified date. No float is permitted in either direction. |
| Near-critical activity | An activity with low but non-zero total float, typically defined by a project-specific threshold (e.g., fewer than 10 working days), that is at risk of becoming critical if any delay occurs. |
| Out-of-sequence logic | A condition where an activity’s recorded progress does not follow the planned logical relationships in the network — for example, a successor activity starts before its predecessor is complete. |
| Path convergence | A schedule condition where multiple activity paths merge into a single activity or milestone. The merge point is exposed to the cumulative risk of delays from any converging path — see also Merge bias. |
| Performance measurement baseline | The approved, integrated scope, schedule, and cost baseline against which actual project performance is measured using earned value management (EVM) methods. |
| Predecessor | An activity whose start or finish constrains the start or finish of a following activity. The predecessor drives the successor through a logical relationship. |
| Probabilistic branching | A Monte Carlo simulation technique where the occurrence of certain activities (e.g., rework loops) is modelled as conditional on a specified probability, rather than assumed to always occur. |
| Progress override | A scheduling calculation mode where an in-progress activity advances based on its remaining duration, ignoring incomplete predecessors. Compare with Retained logic. |
| Resource | Any person, equipment, material, or facility required to perform project activities. Resources may be assigned to activities to drive duration (resource-driven scheduling) or to manage loading. |
| Resource levelling | The process of adjusting activity start and finish dates — within available float — to smooth resource demand over time and eliminate resource overloading. |
| Retained logic | A scheduling calculation mode where in-progress activities with out-of-sequence progress still respect their original network logic. The most technically rigorous mode. Compare with Progress override. |
| Risk | An uncertain event or condition that, if it occurs, has a positive (opportunity) or negative (threat) effect on one or more project objectives, including the schedule. |
| Rolling wave planning | A progressive elaboration technique where near-term work is planned in detail while future work is planned at a higher level. Detail is added to later phases as the project progresses and information matures. |
| Schedule narrative (Basis of Schedule) | A document accompanying the project schedule that explains the scheduling methodology, key assumptions, constraints, logic rationale, resource approach, and any deviations from the project plan. |
| Schedule risk analysis (SRA) | A quantitative technique used to evaluate the probability of achieving project schedule milestones. Typically uses Monte Carlo simulation to model activity duration uncertainty and the effect of risk events. |
| Slack | Synonymous with float. The amount of time an activity can be delayed without impacting the project end date (total slack) or the next activity’s early start (free slack). The term is used in Microsoft Project; “float” is used in Primavera P6. |
| Start no earlier than (SNET) | A date constraint specifying that an activity cannot start before a specified date. Constrains the early start but does not affect the late start. |
| Start no later than (SNLT) | A date constraint specifying that an activity must start on or before a specified date. Constrains the late start and may reduce total float. |
| Start-to-finish (S–F) | A rarely used logical relationship where the successor cannot finish until the predecessor has started. Most applicable in just-in-time scheduling scenarios. |
| Start-to-start (S–S) | A logical relationship where the successor cannot start until the predecessor has started. Often combined with a lag to represent a minimum overlap between activities. |
| Statement of work (SOW) | A formal document defining the work scope, deliverables, timeline, acceptance criteria, and performance standards for a project, phase, or contract. |
| Status date | The date as of which a schedule is updated to reflect actual progress. Also called the data date or time now. Progress is recorded up to this date; remaining work is forecast beyond it. |
| Statusing | The process of updating a project schedule to reflect current progress — including actual start/finish dates, remaining durations, and percent complete — as of the status date. |
| Successor | An activity whose start or finish is driven or constrained by a preceding activity (the predecessor) through a logical relationship. |
| Summary activity | A parent activity in a hierarchical WBS structure that summarises the dates, durations, and progress of its subordinate detail activities. Also known as a hammock activity or WBS summary element. |
| Summary schedule | A high-level schedule showing only key milestones, phases, or summary activities. Used for executive reporting, stakeholder communication, and contract milestone tracking. |
| Total float | The total amount of time an activity can be delayed without delaying the project completion date. Calculated as Late Finish − Early Finish (or Late Start − Early Start). |
| Vertical traceability | The ability to trace a schedule activity from the programme or summary level down through intermediate levels to the detailed level, ensuring consistency of scope, logic, and dates across all schedule tiers. |
| Work Breakdown Structure (WBS) | A hierarchical decomposition of the total project scope into progressively smaller, manageable components — from major deliverables down to individual work packages — forming the structural basis of the project schedule. |
| Work package | The lowest level of the WBS at which cost and schedule can be estimated, assigned, and managed. Typically assigned to a single responsible party and traceable to one or more schedule activities. |