A metric prefix denoting 1,000,000,000,000,000 (one quadrillion, or 1015) units. In computing, peta- refers to 250, and one petabyte (PB) of storage (should such a thing exist some day) is approximately equal to one quadrillion bytes of data (actually 1,125,899,906,842,624 bytes). See also Kilo- and Mega-, Giga-, Tera-, and Exa-. Peta- is usually abbreviated P.