It means just what it says. It's the parity of the contents of A. Nothing more, nothing less.

If you use EVEN parity, the number of 1's in A plus the P bit should be an EVEN number. For ODD parity, the number of 1's in A plus the P bit should be an uneven number.

For more (hystorical) information on parity (why use, how to use, when to use) search Google.