PM Glossary
WBS, Gantt charts, CPM, EVM — the core vocabulary of PMBOK®-style project management, with direct definitions and practical examples.
WBS Structure
- WBS (Work Breakdown Structure)A WBS (Work Breakdown Structure) is a hierarchical, deliverable-oriented decomposition of a project's total scope. Everything the project must produce lives somewhere in this tree.
- Work PackageA work package is the lowest-level node of a WBS — the smallest unit at which cost and duration are estimated and progress is measured.
- 100% RuleThe 100% Rule says a parent node's scope must equal exactly 100% of its children's scope combined — nothing missing, nothing counted twice.
- WBS DictionaryA WBS Dictionary records each WBS node's definition, deliverables, and acceptance criteria. The tree shows what exists; the dictionary answers what each item exactly is.
- DeliverableA deliverable is a verifiable output the project produces and hands over. It is the unit a WBS decomposes around — not the activity, but what the activity leaves behind.
- PhaseA phase is a major management segment of the project life cycle — analysis, design, build, transition — each holding a different character of work and its own deliverables, usually closed by a review gate.
- WBS CodeA WBS code is the hierarchical number — like 1.2.3 — that names a node's position in the tree. It is an address people use, not the node's identity.
- Rolling Wave PlanningRolling wave planning details near-term work finely while leaving far-term work coarse, decomposing each block as its start approaches.
- Progressive ElaborationProgressive elaboration is the planning principle that plans are refined iteratively as information accumulates — detailing within approved scope, which is what separates it from scope creep.
- Control AccountA control account is a management control point at a middle tier of the WBS where scope, budget, schedule, and actuals integrate and EVM performance is measured.
- Planning PackageA planning package holds work under a control account whose scope and budget are known but whose detailed activities are not yet defined.
Schedule & Dependencies
- Gantt ChartA Gantt chart plots tasks on the vertical axis against time on the horizontal, drawing each task's duration as a bar. It is the standard view for comparing the plan with actual progress on one screen.
- MilestoneA milestone is a zero-duration event on the schedule — not work, but a point marking that a moment like "acceptance sign-off" has been reached.
- DependencyA dependency is the logical predecessor-successor relationship between two tasks. Four types — FS, SS, FF, SF — plus lead and lag intervals describe the logic of a schedule.
- Finish-to-Start (FS)Finish-to-Start (FS) means the successor cannot start until the predecessor finishes. It is the default of the four dependency types and covers the large majority of real-world links.
- Start-to-Start (SS)Start-to-Start (SS) means the successor cannot start until the predecessor has started — a relationship that constrains the kickoff moment while allowing the two tasks to run in parallel.
- Finish-to-Finish (FF)Finish-to-Finish (FF) means the successor cannot finish until the predecessor finishes. It expresses work that accompanies a main task and closes together with it.
- Start-to-Finish (SF)Start-to-Finish (SF) means the successor cannot finish until the predecessor has started. It is the rarest of the four types, used for handovers and cutovers.
- LeadLead is time that pulls a successor earlier so it overlaps its predecessor. It is written as a negative interval on a dependency, most typically FS-5d.
- LagLag is deliberate waiting time placed between a predecessor and a successor — a span where nobody works but time must pass, written on the link as FS+3d.
- Critical PathThe critical path is the longest chain of tasks that determines the project finish date. A one-day slip on this path slips the whole project by one day.
- CPM (Critical Path Method)The Critical Path Method (CPM) computes each task's feasible dates and float by sweeping the dependency network once forward and once backward.
- Float (Total Float)Float (total float) is the maximum number of days a task can slip without pushing the project finish date. It is computed as LS-ES; normally zero float puts a task on the critical path, and it can go negative when constraints collide with the logic.
- Free FloatFree float is the number of days a task can slip without delaying even the earliest start of its immediate successor — a narrower notion than total float, which is measured against the project finish.
- Schedule ConstraintA schedule constraint ties a task's start or finish to a calendar date rather than to predecessor logic. Must Start On is the most common form; the rule of thumb is to keep constraints to externally imposed dates only.
- Project CalendarA project calendar defines working days, non-working days, and exception dates. Every date in schedule computation is counted in this calendar’s working days.
- Summary TaskA summary task is a parent row that represents its children as a group. Its start, finish, and progress are derived from the children, never entered directly.
- DurationDuration is the number of working days from a task’s start to its finish. It differs from effort, the total labor invested, and a milestone’s duration is 0.
EVM & Progress
- EVM (Earned Value Management)Earned Value Management (EVM) expresses planned value (PV), completed value (EV), and actual cost (AC) in one cost unit to read a project's schedule and cost performance as numbers.
- PV (Planned Value)Planned Value (PV) is the value of work that should be complete by a given date according to plan — the approved baseline schedule, accumulated over time along the value axis.
- EV (Earned Value)Earned Value (EV) is the value of work actually completed by a given date — counted not as money spent or hours worked, but as the planned value of outputs that passed their completion criteria.
- AC (Actual Cost)Actual Cost (AC) is the money actually spent by a given date — real spend plus effort converted to cost, regardless of what got completed.
- SPI (Schedule Performance Index)The Schedule Performance Index (SPI) is earned value (EV) divided by planned value (PV). At 1.0 the project earns value on plan; below 1.0, value is completing slower than planned.
- CPI (Cost Performance Index)The Cost Performance Index (CPI) is earned value (EV) divided by actual cost (AC). At 1.0 the project earns value on budget; below 1.0, spend is outrunning completed value.
- EAC (Estimate at Completion)The Estimate at Completion (EAC) is the projected final cost of a project, extrapolated from performance to date. The canonical formula divides the total budget (BAC) by CPI.
- S-CurveAn S-curve plots cumulative value or cost against time. Projects typically start slow, accelerate through the middle, and taper at the end — hence the S shape.
- SV (Schedule Variance)Schedule Variance (SV) is earned value (EV) minus planned value (PV). Negative SV means less value is complete than was planned through the status date — the schedule is behind.
- CV (Cost Variance)Cost Variance (CV) is earned value (EV) minus actual cost (AC). Negative CV means spend is outrunning completed value — the project is overrunning its budget.
- BAC (Budget at Completion)BAC (Budget at Completion) is the total approved budget for all project work. Every EVM forecast formula — EAC, VAC, TCPI — anchors on this constant.
- ETC (Estimate to Complete)ETC (Estimate to Complete) is the expected cost of finishing the remaining work. By definition ETC = EAC − AC; the canonical formula is (BAC − EV) ÷ CPI.
- VAC (Variance at Completion)VAC (Variance at Completion) is the budget at completion (BAC) minus the estimate at completion (EAC). Negative VAC forecasts finishing over budget on the current trajectory.
- TCPI (To-Complete Performance Index)TCPI (To-Complete Performance Index) is the cost efficiency the remaining work must sustain to finish within the remaining budget: (BAC − EV) ÷ (BAC − AC).
Planning & Control
- BaselineA baseline is an immutable snapshot of the approved plan. Everything that happens afterward — actuals and changes alike — is measured against this reference.
- Change RequestA Change Request (CR) is a formal proposal to modify a document, deliverable, or baseline. The change lands only after impact assessment and an approval decision.
- Risk RegisterA risk register is the managed list of identified risks, each with probability, impact, and a response plan — the central repository where the results of identification, analysis, response, and monitoring are recorded.
- Progress (Percent Complete)Progress (percent complete) states how finished a task is as a percentage. The number means something only when a measurement method defines what completion is.
- Scope CreepScope creep is the uncontrolled growth of project scope without matching schedule or budget adjustment — an accumulation of small requests that quietly splits actual work from approved scope.