Substantial Completion
The point in a project when the work is complete enough for the owner to use the building for its intended purpose, even though minor items, the punch list, still need to be finished.
Why it matters
It's a specific legal and financial milestone, not just a feeling that things are "mostly done." Substantial completion is usually when warranties start counting down and retainage starts releasing, though actually moving in still depends on a separate [[concept-certificate-of-occupancy|certificate of occupancy]], so the exact substantial completion date matters even before anyone can legally use the space.
On a real project
A new office building's walls, systems, and finishes are all complete and the space is fully usable, but a handful of touch-up paint spots and one slow-closing door remain. The architect certifies substantial completion, and the punch list becomes the remaining short list of work.
Who this matters most to
A Project Manager pushes hard for an official substantial completion date, since it usually triggers a big milestone payment. A Superintendent has to be confident the building is actually safe and usable before agreeing to it; the date isn't just a formality.
Where this goes wrong
A contractor pressures the architect into certifying substantial completion so retainage releases and the warranty clock starts, even though the fire alarm system isn't fully functional yet. The certification turns out to be premature: the fire marshal's own inspection catches the same problem before a certificate of occupancy can be issued, delaying the owner's actual move-in and leaving the rushed certification looking dishonest in hindsight.