P6 Glossary

P6 scheduling glossary

25 scheduling terms in plain field language. No jargon for jargon's sake.

Activity: One chunk of work with a start and a finish, like “Pull feeders, Level 2.” The smallest thing the schedule tracks.
WBS (Work Breakdown Structure): How the job is broken down: building, floor, area, system. The filing cabinet the activities live in.
Milestone: A zero-duration point in time, like “Permanent power energized.” It marks that something is done, not the work itself.
Duration: How many workdays an activity takes. Think crew days, not calendar days.
Calendar: The days and hours work can happen. A 4x10 and a 5x8 calendar give different finish dates for the same duration.
Relationship (logic): The tie between two activities that says what has to happen first. No logic, no schedule.
Finish-to-Start (FS): The next activity can't start until this one finishes. Drywall can't start until rough-in inspection passes.
Start-to-Start (SS): The next activity can start once this one starts, usually with a lag. Pull wire a few days after conduit starts.
Lag: Built-in wait time on a relationship. Use it for real waits like concrete cure, not to hide a missing activity.
Predecessor / Successor: The work before this activity, and the work after it.
Open end: An activity with no predecessor or no successor. A loose wire. It breaks the critical path.
Critical path: The longest chain of tied-together work through the job. Slip anything on it and the finish date slips.
Total float: How many days an activity can slip before it pushes the project finish. Zero or negative means no room.
Free float: How many days an activity can slip before it bumps the very next activity.
Negative float: The schedule already says you'll miss a date. A warning light, not a math error.
Constraint: A date forced onto an activity, like “Start No Earlier Than.” A few are fine. Lots of them mean the logic isn't doing its job.
Data date: The “as of” line. Everything before it is history (actuals). Everything after it is forecast.
Schedule (F9): The P6 command that recalculates dates from logic, durations, and the data date.
Baseline: A saved copy of the approved plan. You measure progress and delays against it.
Update / status: Entering actual starts, finishes, and remaining durations as of the data date. The weekly job of a scheduler.
Remaining duration: How many workdays are really left. Ask the foreman, not the percent-complete column.
Percent complete: How far along an activity is. P6 has several types, so know which one your project uses.
Resource loading: Assigning labor, equipment, or cost to activities so the schedule shows manpower curves, not just dates.
Leveling: Letting P6 shift activities so resources aren't overbooked. Powerful, and easy to misuse.
XER: P6's export file format. How schedules get shared between companies and tools like Raziel.