A) An extra bit appended to a character as an accuracy check.

For example, if parity is even, the sum of all 1s in the character should be even. b) Number of 1s in a word, which may be even or odd. When parity is used, an extra bit is used to force the number of 1s in the word (including the parity bit) to be even (even parity) or odd (odd parity). Parity is one of the simplest error detection techniques and will detect a single-bit failure.