par·sec / ˈpärˌsek/ (abbr.: pc) • n. a unit of distance used in astronomy, equal to about 3.25 light years (3.08 × 10¹⁶ meters). One parsec corresponds to the distance at which the mean radius of the earth's orbit subtends an angle of one second of arc.

parsec (pc) Distance at which a star would have a parallax of one second of arc; equivalent to 3.2616 light years, 206,265 astronomical units, or 3.0857 × 10¹³ km.