In general, parity is the quality of being even or odd. In computer science, a parity check, also referred to as a Vertical Redundancy Check (VRC), is a method of searching data for errors either during transmission or on a storage mechanism. The check is based on a parity bit, a single bit of metadata indicating whether the sum of the data bits is even or odd. For example, if a binary stream contains an even amount of "1's" and the parity bit is odd, the computer would produce an error because the data is corrupted. The image to the right shows 7-bit binary numbers with an eighth parity bit attached.
In the past, most memory manufacturers offered both parity and non-parity RAM chips, with parity RAM using a ninth parity bit for every eight-bit byte. Modern computers which require error-checking at the hardware level typically use ECC RAM, which uses a more complex form of error checking.