Real Dictionary

parsec in American English
a unit of distance, usually used to measure the distance to a star, equal to 206,265 astronomical units (3.0857 x 1013 kilometers or 1.92 x 1013 miles or 3.2616 light years): it is the distance at which an angle of 0° 0′ 1″ (one second of arc) would form
noun: a unit of distance equal to that required to cause a heliocentric parallax of one second of an arc, equivalent to 206,265 times the distance from the earth to the sun, or 3.26 light-years

parsec in British English
noun: a unit of astronomical distance equal to the distance from earth at which stellar parallax would be 1 second of arc; equivalent to 3.0857 × 1016 m or 3.262 light years