How does parity check work for error detection?

Parity check adds one bit to data to make the total number of 1s either even (even parity) or odd (odd parity). The receiver checks if received parity matches expected; mismatch indicates error. Simple parity detects single-bit errors but cannot detect even numbers of errors or locate error position. Two-dimensional parity (adding row and column parities) can detect and correct single-bit errors. While simple, parity is used in memory systems (ECC DRAM uses more sophisticated codes) and basic error detection applications.