Comment by eduction

It goes beyond a foldable, can be applied to streams. Clojure had foldables, called reducers, this was generalized further when core.async came along - transducers can be attached to core async channels and also used in places where reducers were used. The terminology is used to document the thing that various contexts accept (chan, into, sequence, eduction etc). They exist to make the language simpler and more general. They could actually allow a bunch of old constructs to be dispensed with but came along too late to build the whole language around.