What is a light year??????????
A light-year is a distance.
It's the distance that light travels through vacuum in one year.
The distance is 9.4607 x 10¹² kilometers in metric units, and 5.8786 x 10¹² miles
in 'customary' units, and is normally written without a bunch of question marks.
A light year is an unit of distance.
[latex] light year[/latex] ≈ [latex]10^1^3km[/latex]