Emerging at around the same time as "Classic Trance" the two are pretty interchangeable with a great deal of cross over. House music at the end of the 80's and beggining of the 90's had gone a little aray due to its explosion earlier in the decade having much wider effect than expected. So, while House was looking a little lost at this point, Acid Trance evolved out of Acid House to try to breeth some life back into things, which it did. House later re appeared in the form of Progressive Trance.

Acid was the best thing that happened to trance. Acid's wet, squelchy, bubbley sound makes it very hard to predict and determine what its going to do next. Being so free allowed one to become entranced