Debut of, or release date for, a pop song or record album. Slang. Less common synonym: break
"Soul Train: When does the album drop?
Ryan: Actually, now, we don't have a set date...
What's the next single, and when does it drop?"
-- Soul Train, interview with Ryan Toby of City High, taped 4/8/01, http://www.soultrain.com/st/cityhigh.html.
"...Eminem's third album was pushed from its original drop date and formally released Sunday..."
-- MTV News, 05/29/2002, http://www.mtv.com/news/articles/1454573/20020529/eminem.jhtml?headlines=true.
Does not refer to a drop in the song or album's popularity or chart position, in fact, the album "drop" often coincides with its highest popularity.