The parsec (symbol pc) is a unit of length used in astronomy. The length of the parsec is based on the method of trigonometric parallax, one of the oldest methods for measuring the distances to stars. The name parsec stands for "parallax of one second of arc", and one parsec is defined to be the distance from the Earth to a star that has a parallax of 1 arcsecond. The actual length of a parsec is approximately 3.086×1016 m, 3.262 light-years or 19,176,075,967,324.937 miles.
Full article HERE. Full definition of 'light year' HERE.