Flanger
The sound of a jet engine passing through a guitar — a comb filter whose teeth sweep up and down.
The name is a leftover from the tape era. Two machines played the same recording in sync, and the engineer slowed one down by pressing a finger against the rim of the reel — the flange. The few milliseconds of offset produced a comb filter, and as the finger eased off, the notches swept across the spectrum. The Small Faces' "Itchycoo Park" (1967) is the textbook example.
Digitally it's trivial: a delay of roughly 1–10 ms whose length is modulated by an LFO, mixed back with the dry signal. Feedback deepens the notches and makes it more metallic. The difference from chorus is mostly a matter of numbers — chorus uses longer delays and no feedback, so it sounds like more players rather than an aircraft. "Through-zero" flanging, where the copy actually overtakes the original, was for years the one thing tape could do and plugins couldn't.