Dismemberment is the act of mutilating a body via removing the limbs, usually done after death it can also be done as a type of torture and is very common after murders as the criminal often has to resort to dismembering a body in order to discard it without alerting authorities.
Some killers also gain personal enjoyment and even sadistic "highs" from dismembering their victims - these types of killers tend to be amongst the most brutal and vicious, for obvious reasons.