Wave function collapse
Also said as WFC, Model synthesis
Fill a grid with tiles that have rules about what may sit next to them. Each cell starts as anything; pick the most certain, decide it, and let the rules narrow its neighbours. Repeat.
You describe what fits together, not how to build it, and a small tileset gives endless varied results that always obey the rules. If a cell runs out of options you have to back up or start again.
Say it
“Generate the dungeon with wave function collapse: 30 tiles with socket rules on each edge. Restart on a contradiction, and bias the weights towards corridors.”
Where you’ve seen it
Maxim Gumin published the algorithm in 2016. Oskar Stålberg used it in Bad North, and in a different way in Townscaper, where it works out which pieces fit the shape you have just clicked.
Not to be confused with perlin noise
Noise gives you smooth values and knows nothing about the things you place. Wave function collapse knows only about what can sit next to what.