DCT compression
From Just Solve the File Format Problem
DCT compression (Discrete cosine transform) is a compression technique used for images and audio. It is used in JPEG and (in a modified form) MP3, where it provides lossy compression (meaning that some detail is lost).
The audio format known as DCT is, however, not related; that abbreviation comes from "dictation". That format can use a variety of codecs including MP3, meaning that it might or might not happen to use the compression technique with the same initials.
