A parity bit is a simple error detection mechanism used in digital communication and data storage. It is an extra bit added to a binary number to ensure that the total number of 1s is either even or odd, depending on the chosen parity scheme. For example, in even parity, the parity bit is set so that the total number of 1s in the byte is even. When data is transmitted or stored, the receiving system checks the parity bit to verify the integrity of the data. If the calculated parity does not match the expected parity, it indicates that an error may have occurred during transmission or storage. This method is commonly used in systems like computer memory and network communication.