Parsecs

From The Encyclopaedia Expurgatia

A parsec is the distance between the casual observer and an object [usually a star] which has a parallax of one arcsecond. Trigonometry aside, it's about 206,265 Astronomical Units, 30,859 terametres, 3.2616 lightyears, or 19,173,500,000,000 miles.

Parsecs are not to be confused with parsex, which is the trigonometric computation of fornication with precisely the allowed number of mistakes.