A lightyear is a unit of distance that is used in astronomy. It's about the distance that it takes for light to travel one year.
The lightyears away galaxy is very large.
The lightyears that it took for the signal to reach us was very long.
noun
A unit of length (abbreviation ly; equal to just under 10 trillion kilometres (1016 metres)) equal to the distance light travels in one Julian year; used to measure extremely large distances.
noun
(only in plural) A very long way.
noun
(only in plural) A very long time.