Peta-

Peta is a unit prefix in the metric system denoting multiplication by 1015 (1  000  000  000  000  000). It was adopted in the International System of Units in 1975, and has the symbol P.

Peta is derived from the Greek πέντε, meaning "five". It denotes the fifth power of 1000 (10005). It is similar to the prefix penta ("five"), but without the letter n (on the analogy of the prefix tera (from the Greek for "monster") for 10004 looking like tetra- ("four") with a letter missing).

Examples:
 * 1 petametre = 1015 metres
 * 1 petasecond = 1015 seconds (31,7 million years)
 * 1 petabyte = 1015 bytes
 * the mass–energy equivalence is 89.9 PJ/kg
 * 1 light-year = 9.461 Pm