Procedural generation
Creating content — levels, terrain, textures — with algorithms at build or run time instead of placing every element by hand.
You trade authored detail for a seed and a ruleset; the same seed reproduces the same world, so a game can ship a near-infinite map in a few kilobytes. Roguelikes (Rogue, 1980) did it early out of sheer memory scarcity, and Elite (1984) fit eight galaxies of 256 star systems each into a BBC Micro by generating them from a Fibonacci-like sequence. No Man's Sky (2016) pushed the idea to some 18 quintillion planets.
The risk is sameness — purely random output feels like noise, so modern procedural generation layers noise functions, grammars and constraint solvers like wave function collapse over hand-authored building blocks. The craft lives in the constraints, not the randomness.