Peta (symbol: P) is a prefix in the SI system of units denoting 1015, or 1 000 000 000 000 000.
In computer science peta can sometimes mean 1 125 899 906 842 620 (10245 or 250), instead of 1 000 000 000 000 000, especially when used to prefix the byte, giving a petabyte.
wikipedia.org dumped 2003-03-17 with terodump