In asynchronous communication systems, odd parity refers to parity checking modes, where each set of transmitted bits has an odd number of bits. If the total number of ones in the data plus the parity bit is an odd number of ones, it is called odd parity. If the data already has an odd number of ones, the value of the added parity bit is 0, otherwise it is 1.

Parity bits are the simplest form of error detection. Odd parity checking is used in testing memory storage devices. The sender and receiver should agree to the use odd parity checking. Without this, successful communication is not possible. If an odd number of bits are switched during transmission, parity checks can detect that the data is corrupted. However, the method will fail to detect errors introduced when an even number of bits in the same data unit is altered, as the parity will still remain odd despite data corruption.