Cyclic Redundancy Check

CRC is a trick to verify if the bits are transmitted correctly.
Calculate the CRC of the data you want to transmit.
Send both the data and this checksum to the receiver.
The receiver does the same calculation on the data and compares this with the checksum.
The result of the calculation and the checksum should be the same.
If not, part of the data (or the number itself) is mangled.

1. Cyclic redundancy check - Wikipedia