CRC - Cyclic Redundancy Check
Cyclic Redundancy Check is the simplest but tremendous error detection technique used by networking and storage devices. The technique is quite useful to detect error in a "digital" data. The CRC error while copying data on a hard drive indicates a bad sector.
In CRC, the algorithm runs on the data at the source and calculates some value, say 'x'. At the destination, the same algorithm runs on the received data and the calculated value is compared with the value of x. If the calculated value at the receiver's side matches with the received value x, the content is accepted. The distinction in the value of x indicates an "error".
Sometimes the corrupted block could be rectified using any specific algorithm, or the complete message needs to be re-sent.