A feral cat is a cat who has either never had any contact with people or her contact with people diminished over time. They are not socialized and cannot be touched, except sometimes by the people that feed them.
The ideal window for socializing a feral kitten is 12 weeks of age or younger. Beyond that it is very difficult to tame them and they may never socialize. Trying to tame them at that age is dangerous and stressful. Feral cats live happy lives outdoors and the best thing that can be done for them is to leave them and Trap-Neuter-Return.