A palisade is a heavy-duty fence that's strong enough to keep out intruders, like one you might see around a military camp.
Traditionally, palisades were built with wooden stakes around small forts or castles as a way to keep out enemies. There's evidence that this kind of fence was often used in ancient Greece and Rome. More modern palisades are made out of metal and give protection to houses in dangerous neighborhoods, for example. The root word is the Latin palus, which means "stake."