A bit (0 or 1) added to a binary number (such as 1001100) to help check if the number is received correctly.

For **even parity** all the "1" bits are counted:

• if the count is odd then the parity bit is set to 1 (making an **even number of 1s**)

• if the count is even then the parity bit is set to 0 (also an **even number of 1s**)

Examples:

1001100 has an odd number of 1s, so the parity bit is set to 1, giving 1001100**1**

1010011 has an even number of 1s, so the parity bit is set to 0, giving 1010011**0**

So, including the parity bit, all binary numbers will have an even number of 1s.

If we receive a number that breaks this rule then some error happened and the number can be sent again.

There is also **odd parity**: same idea, but the parity bit is set to always have an odd number of 1s.

Note: this is a good way to check if there is a single error in the number, but won't work if there are two errors!