TIL extrusion, or more commonly FDM, is only one kind of 3D printing.
I don't remember what led me to this rabbit hole, but I came across stereolithography, which is a kind of 3D printing that uses photopolymerization to cure a pattern, layer after layer, in liquid resin with light.1
That got me curious about other types on 3D printing and I came across SLS, which is a kind of powder bed fusion, and works exactly like it sounds: a pattern is fused, layer by layer, in powder with a laser.2
The real phase shift (lul) for me was thinking of 3D printing as additive manufacturing which I don't automatically associate with filament printing.
Anyway, this video does a good job describing SLS.
Footnotes
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most commonly afaict the light is emitted from a grid which has a resolution exactly like the resolution we give to computer screens. ↩
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the artifact, by the end of a print, is buried in powder and makes the whole process seem like archeology ... which is probably annoying, but pretty awesome at the same time. ↩