Fishing bots are players or gold farmers that use third party software to automatically fish for them in order to get either a high fishing level or profit, usually the latter. They directly break the macroing rule under Honour, and players caught using fishing bots will generally receive a permanent ban.
It is STRONGLY advised to NOT download any macroing software, as the chances of being caught by Jagex are extremely high, and NOT worth risking your account and/or your hard-earned skill levels for.
Fishing bots often hang out in Catherby and the fishing guild when found in members, and Karamja and Draynor Village in free worlds (the bots in Karamja will bank their fish using the fisherman to the south to turn their fish into bank notes or in Draynor Village via the boat in Port Sarim). Most bots fish lobsters and sharks, which they sell for coins, and then sell the coins for real world cash in direct violation of the real-world trading rule under Honour (formerly Rule 12). Although most fishing bots sell their collected fish raw, some of them have also been known to cook their collected fish, though this has been rare unless they are botting more of their stats.
Fishing bots were extremely rare due to the December 10, 2007 update. Since the free trade update on February 1st, 2011 they have become more common for people to gain fast money on garbage accounts and transfer it to their main accounts. They usually have either a randomized or the default look, and will often have random or Asian names (since Jagex claims that bots are normally operated by sweatshop workers in East Asian countries). On F2P worlds, they are usually level 3-10. On members worlds, they are usually around 30 combat. Now however you can see bots of all levels training their fishing regardless of the consequences if they are caught. Due to recent updates which brought back free trade, bots of all types are becoming more common, although Jagex bans thousands of accounts for macroing every day.