A style of techno/house music, noted for its prominent use of the of the Roland TB-303, a synthesizer with a distinctive (and very funky) sound. Variants include hard acid, acid house, acid trance, etc. Not all music that includes a 303 is necessarily acid, and not all acid music makes use of the 303 (but most of it does).
Some suggest that the word is derived from the phrase "acid burn" - a slang term from the early days of house music, referring to the practice of sampling from another musician's records (see bite).
Others cite a 1985 house single by Phuture called "Acid Trax", which is recognized as one of the first house records to make use of the 303.
A more concrete theory is that it refers to the drug LSD, which is commonly used at raves where acid house is played. Given the psychedelic nature of acid house, this interpretation is certainly part of the popular understanding of the term, if not necessarily its historic origins.
Drum & bass is okay, but what I really want to hear is some nice tweaky acid.
By Greenie