1. An Internet user that leeches off ISPs — the sort you can never provide good enough services for, always complains about the price, no matter how low it may be, and will bolt off to another service the moment there is even the slimmest price difference. While most bottom feeders infest free or almost free services such as AOL, MSN, and Hotmail, too many flock to whomever happens to be the cheapest regional ISP at the time. Bottom feeders are often the classic problem user, known for unleashing spam, flamage, and other breaches of netiquette.
2. Syn. for slopsucker, derived from the fishermen's and naturalists' term for finny creatures who subsist on the primordial ooze. (This sense is older.)