APL: Acronym for "A Programming Language."

Kenneth E. Iverson developed Iverson notation in the late 1950s, joined IBM in the early 1960s, and then developed APL from Iverson notation. APL is notable in that it uses a tremendous (and non-ASCII) character set.

APL is traditionally considered succinct to the point of impenetrability. While some modern languages such as the various LISP dialects allow the same sort of peculiarities that led to APL's extreme terseness-- functions taking other functions as parameters only to return an array of functions, for example-- most modern coders avoid them since they tend to lead to unmaintainable code. (APL is sometimes described as a "write-only language"-- it takes a tremendous amount of effort to look at a line of APL code and figure out what it's meant to do, let alone what it actually does.)