Unlike a normal failure, in which a character merely fails to achieve their desired result, a botch has actively negative consequences. For example, botching a roll when shooting a gun may result in the gun jamming, rather than merely missing the target, while botching a roll to disarm a security system might trigger the alarm or even result in the character getting an electrical shock from the system. The exact details are usually left up to the Storyteller to decide.
In the original Storyteller System, a botch occurred when a character rolled more 1s than successes on a roll. This actually made botches more likely for characters with large dice pools when the difficulty of the roll was high. In the Revised Storyteller System, this was changed so that a botch only occurred when a roll garnered at least one 1 and no successes at all. This botch mechanic was used in the Revised Edition games using the Storyteller System.
In Werewolf: The Wild West, a botch is referred to as a "misfire".