Algorithmic reverb
Reverberation computed by a network of delays and filters rather than captured from a real room.
Manfred Schroeder at Bell Labs showed in 1962 that parallel comb filters followed by allpass filters produce something that sounds like a room. Later designs, notably the feedback delay networks of the 1990s, mix several delay lines through a matrix for a denser, less metallic tail. Every parameter — size, decay time, high-frequency damping — is freely adjustable, so impossible spaces are as easy as cathedrals.
The EMT 250 of 1976 was the first commercial digital reverb, and the Lexicon 224 of 1978 was the one you heard on half the records of the 1980s. The opposite approach is convolution reverb, which reproduces a real space exactly and, for that very reason, is much harder to bend.