a unit of distance, usually used to measure the distance to a star, equal to 206,265 astronomical units (3.0857 x 10 kilometers or 1.92 x 10 miles or 3.2616 light years): it is the distance at which an angle of 0° 0′ 1″ (one second of arc) would form a triangle having an opposite side with a length of one astronomical unit: abbrev. pc