parallax second

Wiktionary

1. n. A unit of length used to measure the distances of stars from Earth, defined as the distance from the Earth of a star that has a parallax of 1 arcsecond. Approximately = 3.08568025 × 1016 meters = 3.2616 light-years.

GNU Webster's 1913

1. n. An annual parallax of one second of an arc; -- applied to celestial objects outside the solar system. It is used to measure the distance of an astronomical object from the Earth. A star which has an annual parallax of one second of an arc is considered to be one parsec (3.26 light years) distant from the earth. See parsec in the vocabulary.