1. a digit representing the sum of the digits in an instance of digital data; used to check whether errors have occurred in transmission or storage;

WordNet (r) 3.0 (2006):

checksum n 1: a digit representing the sum of the digits in an instance of digital data; used to check whether errors have occurred in transmission or storageThe Free On-line Dictionary of Computing (18 March 2015):

checksumA computed value which depends on the contents of a block of data and which is transmitted or stored along with the data in order to detect corruption of the data. The receiving system recomputes the checksum based upon the received data and compares this value with the one sent with the data. If the two values are the same, the receiver has some confidence that the data was received correctly. The checksum may be 8 bits (modulo 256 sum), 16, 32, or some other size. It is computed by summing the bytes or words of the data block ignoring overflow. The checksum may be negated so that the total of the data words plus the checksum is zero. Internet packets use a 32-bit checksum. See also digital signature, cyclic redundancy check. (1996-03-01)