What is "parallax second"

parallax second \par"al*lax sec"ond\, 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.

n. A unit of length used to measure the distances of star 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.