It means recorded music, particularly when it is a substitute for live music. It's a derogatory word. If you call it "canned music," it means you don't like it. Canned food is preserved. It doesn't taste as good as fresh food. It might be a low-quality substitute for fresh food. Canned music is "preserved" music, and it might be a low-cost substitute for live music. "The restaurant featured a 'jazz dinner' at 8 pm. We arrived early. The musicians weren't there yet, but they had canned music playing to set the mood." "I hate the canned music you hear playing in stores and elevators."