Debut of, or release date for, a pop song or record album. Slang. Less common synonym: break Examples:
"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,
"...Eminem's third album was pushed from its original drop date and formally released Sunday..." -- MTV News, 05/29/2002,
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.