As-built drawings are a marked-up set of drawings showing what was actually constructed, including every deviation from the original design: relocated walls, rerouted ductwork, substituted equipment, hidden utility runs. They are the historical record the owner uses for future maintenance, renovations, and tenant improvements.
The contractor typically maintains a working as-built set in the field throughout construction, redlining the drawings as changes happen. At closeout, the redlined set is delivered to the architect, who incorporates the changes into a clean set of record drawings (often as PDFs and CAD files). Most commercial contracts require as-builts before final payment is released. Skipping or rushing as-builts at the end of a project is one of the most common closeout failures and a frequent reason retainage stays held.