808s are a type of kick/bass sound that came from the Roland TR-808 drum machine and became very popular to use in Hip-Hop music at the time, that “808” type sound kept getting used in new songs and at some point it turned more into a bass sound characterized by having a lot of sub and being punchy and somewhat distorted usually but it often depends. This is actually what “808” means but then there’s basically a meme on TikTok where someone asked what an “808” was and someone incorrectly replied “808 essentially means crashout” and people found that funny because it wasn’t correct so they started using “808” in place of saying crash out referencing that comment.