This isn't an exact definition, but its pretty close:
A stray is a cat who was raised by a human and then abandoned or lost, but still has some trust in humans.
A feral cat is one who has either reverted to a wild state or who was born into the wild and never had human contact.
Even feral cats are domesticated, so they do not survive very long on their own. All domesticated animals need the care of humans to survive.
Did that make sense?