3GP
A heavily compressed MPEG-4 video files intended for playback in a mobile phone or low bandwidth playback, oftentimes it is synonymous with pr0n/porn because before Internet gone wild west, porn is spread from one mobile phone to another, in small file size due to internet speed is extremely abysmal (Dial Up 56kbps or DSL 384kbps)
Ah, good old times when 3GP pr0n makes our imaginations, while HD pron, 4K pron, 8K pron, VR pron, 360 pr0n, or whatever, destroys our imaginations