A cramp is when your pieces do not have much mobility. This usually will arise probably from letting your opponent grab a huge space advantage. It is not good to have a cramp, and it will let your opponent slowly grab more space, squeezing you to death. A master of this technique would be Tigran Petrosian. Space is important. Most people do not like cramps and they are bad. Here is an example:
Cramping your opponent is a deadly weapon and can win you many games! Enjoy!