The Collaborative International Dictionary of English v.0.48:

parity check \par"i*ty check`\, n. (Computers)
   The act or process of testing whether a byte or other data
   structure has an even or odd number of bits set to the value
   of 1; -- it is used primarily to detect errors in data,
   especially in memory banks or in data transmitted over a
   communications line. The parity can be changed by assigning
   one bit in each data structure as the parity bit, so that
   the total number of bits set to the value of 1 is odd (odd
   parity) or even (even parity). If parity is used for error
   checking the writing and reading systems must first agree on
   which type of parity (odd or even) to use; if the reading
   system detects a deviation from the agreed parity, it signals
   an error, to be handled by the error-handling processes of
   the system.
   [PJC]

WordNet (r) 3.0 (2006):

parity check
    n 1: a system of checking for errors in computer functioning
         [syn: parity check, redundancy check, odd-even check]