In slang usage on the Internet, it means to remove, censor, or ban material. Here's the story behind the term, as seen in "The Chronicles of George" (a link to this site is below):
There are one or two individuals who, for whatever reason, enjoy signing up new accounts every single day to post leftist drivel. Sometimes they are vanities from DemocraticUnderground. Sometimes they are articles from other far-left sources. Sometimes they are nothing but vile doctored images or profanity laced tirades. Sometimes they are from legitimate sources but happen to strike the eye of the poster as being something that would infuriate conservatives.
The posters in question always post the articles, and then don't reply. They then post other articles, again not replying. This was going on for months. Jim would confirm by looking at the IP addresses and other aspects of the user's 'footprint' that it was the returning troll, and we would nuke the accounts. This went on for months.
Then some of the opportunists who wanted to harm the forum started a whispering campaign, complaining about articles being deleted. They would play off of the fact that the trolls' articles were being pulled to complain that there was some sort of agenda of squelching legitimate conservative postings going on by the moderators.
One day I decided to try something new. I decided, instead of letting the trolls get what they want and have their posts up as flame bait, and instead of pulling the threads outright, I would move their post aside and replace it with something that hopefully others would find humorous. I would do this out in the forum for all to see. The original piece would be available through the history link for the curious, who could see if there was some sort of censorship campaign going on. And the 'freepers' could have fun mocking the troll if they so liked.
It so happens that the way I did it the first time was using a screen shot from Caddyshack, where the pastor gets hit by a lightning bolt. Being a bit of a fan of the comic strip "B.C." I captioned the photo with the lightning bolt sound that Johnny Hart used in his strip- ZOT! That is where the term Zot originated.
Now, sometimes we "zot", and sometimes we simply pull it. It depends on a number of factors, including how busy we are at the time. But whenever you see a Zot, you can be sure that the user was a newbie who was doing their hit-and-run posting, and that if you as a well-established freeper thought the article would have made an interesting discussion, then you could probably post the same piece yourself without incident (although the most vile of the stuff probably would get pulled, and Jim reserves the right to remove anyone who he feels is constantly trying to push leftist propaganda on the forum). Anyway, that is the history and background behind zotting. Thanks guys!