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:
2. light-years. a.
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.
The distance that light travels in a vacuum in one year, equal to about 9.46 trillion km (5.88 trillion mi). Light-years are used in measuring interstellar and intergalactic distances. Compare astronomical unit, parsec.
The American Heritage® Science Dictionary
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