A feral organism is a plant or animal which has changed from being tame or cultivated to being wild.
A feral animal is one which has escaped from a domestic or captive status and is living more or less as a wild animal. Animals which were wild before they escaped from captivity are not regarded as feral. For example, a lion which has escaped from a zoo is not a feral animal. Some common examples of animals with feral populations are goats, cats, and pigs.