It could be a number of things… depends on the context ;-).
It could be dumping, as in taking a #2, dropping a deuce, etc:
It could be taking a bunch of trash and leaving it somewhere… either legally or illegally:
Or, I assume you’re asking in the VB context. In that case, it’s reading the data off of a cartridge and storing it as a file on a computer. These are the ROM files, or “ROM dumps” that you can play on an emulator, burn to a flash cartridge, hack, keep as a backup in case something happens to the original cart, or anything else you can think of. It’s similar to ripping a music CD, although that usually involves converting the raw data into a format like mp3. A ROM dump is just a raw binary “dump” of the ROM chip in the cartridge.