A feral cat is a domestic cat this is born in the wild and that typically lives in a colony with other feral cats. These cats are typically unable to handled because they have had no exposure to human touch or contact. Kittens born in the wild begin to take on feral behaviors at a very young age and therefore only very young feral cats can be domesticated.
TNR is the humane trapping of feral cats, spaying or neutering them, and returning them to their colony. This program is promoted on a national level by the ASPCA as a more effective way of dealing with feral cat populations.
The ASPCA has a fantastic FAQ page.
In Berks County, there are two organizations that deal with Trap and Return:
Fairchild Foundation: offers TNR clinics on the third Sunday of each month.
No Nonsense Neutering: offers TNR clincs on Wednesdays and Fridays as well as trap rental and feral cat deterrants