ˈlight year BrE AmE noun [countable]
1 . the distance that light travels in one year, about 9,460,000,000,000 kilometres, used for measuring distances between stars:
a star 3,000 light years from Earth
2 . light years ahead/better etc than something informal much more advanced, much better etc than someone or something else:
The Japanese company is light years ahead of its European competitors.
3 . light years ago informal a very long time ago:
It all seems light years ago now.