Won't explain any theory, as you should know it.
However, I'll give some examples of what it is.
If a bit stream has an even number of 1's in it, it has even parity.
e.g.
0110101 = 4 1's.
If a bit stream has an odd number of 1's in it, it has odd parity.
e.g.
0001101 = 3 1's.
Parity...