What is a Feral?

I've been assuming that a feral cat is one who was not born in captivity and has not been handled by humans - never domesticated. Some of the ones we have which fit that description will not let me come even within 4 feet of them when feeding them. Others will let me put food down in front of them, but when I try to touch them carefully they swat with claws out quite fiercely.

Could anyone illumine me on the true definition of feral cat?