Asset pipeline
The toolchain that turns source formats — PSD, FBX, WAV — into engine-ready runtime formats through import, processing, compression and packaging, run as an offline build step.
An artist hands over a 50 MB PSD; the game wants a compressed GPU texture of a few hundred kilobytes. Between them sits the pipeline: it imports the source, generates mipmaps, compresses to a block format, bakes prefabs and packs everything into load-friendly bundles. Unreal calls the final step "cook"; Unity has its import pipeline.
The point is that all the heavy work happens once, ahead of time, not while the player waits. A good pipeline is incremental — change one file and only it rebuilds — and supports hot reload so edits show up live in a running engine. Badly built pipelines are a notorious time sink in game production.