Feral cats are or are descended from domesticated cats.  They were either born into an outdoor life, or were lost or abandoned, and have adapted to living outdoors.   They are not pets, but they are also not wildlife.  They are not socialized to humans, so are not suited to being pets.  Feral cats are not owned, but if they are fortunate, they have caregivers who make sure they are sterilized, ensure they have daily food and water, provide shelter from the elements, and secure veterinary care when they need it.

Several national organizations offer great information on caring for feral cats:

http://www.alleycat.org
http://www.humanesociety.org/issues/feral_cats/tips/what_you_can_do_for_ferals.html
http://www.aspca.org/adoption/feral-cats-faq.html