Feral is just another word for wild. It means that the cats have not been socialized to humans and that they are afraid of people. It does not mean that the cats are aggressive or dangerous. Feral cats run from people. They do not attack unless they are cornered and feel that they have no other alternative but to fight for their lives.

From Alley Cat Allies website:
A feral cat is born and raised outside with little or no human contact or is a stray that has lived outside long enough to revert to a wild state. Adult feral cats usually cannot be tamed and are most content living outside. Feral kittens up to eight or ten weeks of age, on the other hand, can often be tamed and placed in homes.