- the distance traversed by light in one mean solar year, about 5.88 trillion mi. (9.46 trillion km): used as a unit in measuring stellar distances. Abbreviation: lt-yr
- light-years,
- a very great distance, especially in development or progress: The new computer is light-years ahead of the old one.
- a very long time: It's been light-years since I've seen my childhood friends.
- a unit of distance used in astronomy, equal to the distance travelled by light in one year, i.e. 9.4607 × 10 12 kilometres or 0.3066 parsecs
