A shorebot is a now-obsolete type of player-created bot that was used to aid PvP attacks. PvPers once surmised that players were less likely to be buffed -- and therefore more were more likely to be vulnerable -- while they were spending turns at the shore. By constantly refreshing an enemy player's character pane, players could see when their target's turns played increased in increments of 3 and/or their target's meat decreased in increments of 500, both of which indicated that he or she was shoring. A shorebot would constantly refresh a player's profile page, and then initiate a PvP attack when it detected the meat or turns played stats of the player changing in either of the aforementioned ways. This was, at the time, considered a valid PvP strategy.
Similar counter-bots were created; these bots constantly placed 500 meat in a player's closet, in order to give the appearance of shoring. This would hopefully entice an attack that was doomed to fail.
To prevent the unnecessary hits on players' profile pages, Jick changed them so that a player's turns played and meat count would only update once per day. He also famously ranted about the shorebots on Radio KoL. A transcript of his rant can be found here, and you can listen to it here. The rant has also been immortalized in a remix (mirror) by KennethTheObscure. It must be noted that the remix re-arranges Jick's words to create new sentences. For example, Jick never said that "every other person playing the game were shorebots".
The clan Iocaine Powder claims that it did not come up with or use shorebots, contrary to popular belief.