Exploit

An exploit is an error or unintended consequence that, when used, provides an unfair advantage to those players that know about it. In general, being caught using an exploit can be grounds for a temporary ban (the first time you are warned) or a permanent ban if you persist in using it.
For example, and without revealing how to do it, there is an exploit in Siege War that allows targeting and attacking through a closed castle gate. Another (a particular buff) causes opponent's clients to crash.