WordNet (r) 3.0 (2006):

petabyte
    n 1: a unit of information equal to 1000 terabytes or 10^15
         bytes [syn: petabyte, PB]
    2: a unit of information equal to 1024 tebibytes or 2^50 bytes
       [syn: petabyte, pebibyte, PB, PiB]

The Free On-line Dictionary of Computing (30 December 2018):

petabyte

    (PB) A unit of data equal to one quadrillion bytes
   but see binary prefix for other definitions.  A petabyte is
   10^15 bytes or 1000^5 bytes or 1000 terabytes.

   As of 2013-11-05, the Internet Archive Wayback Machine
   contains almost two petabytes of data.

   A petabyte is the amount of data that would be required to store a
   2000 by 1600 pixel image of every one of the 314 million people
   living in the USA in 2012.

   1000 petabytes are one exabyte.

   See prefix.

   (2007-09-13)