Acronym for Error Correcting Codes.
Usually refers to Hamming codes. I never really understood these things, but they work, and I've never had to implement them, so I'm happy.
Also known as:
Error Checking and Correcting. Parity can only detect errors, but ECC can also repair it, assuming that there are only single bit errors now and then. It requires only 30% or such more bits to be transmitted.