An Etymological Dictionary of Astronomy and Astrophysics

A basic unit of astronomical distances, corresponding to a → trigonometric parallax of one second of arc. In other words, it is the distance at which one → astronomical unit (the mean radius of the Earth’s orbit) subtends an angle of 1 arcsecond.
1 pc = 3.2616 → light-years = 206 265 astronomical units = 30.857 x 10¹² km.

See also: From parallax + second.