As-builts (also called record drawings) document what was actually constructed, capturing every deviation from the original contract drawings — a rerouted utility, a relocated wall, a substituted product. They're maintained throughout the job and finalized at closeout.
Accurate as-builts are a required closeout deliverable and are genuinely valuable long after the job: the owner's facilities team relies on them to locate buried utilities, tap into systems, and plan future renovations. Sloppy as-builts are a common closeout headache.