What is the distance that light travels in a year called?

The distance that light travels in a year is called a light-year.

A light-year is a unit of distance, not time. It measures how far light travels through a vacuum during one Julian year, defined as exactly 365.25 days. Because light moves at 299,792,458 metres per second, one light-year equals exactly 9,460,730,472,580.8 kilometres—about 5.88 trillion miles.

Astronomers use light-years to describe enormous distances between stars and other objects beyond the Solar System. For example, Proxima Centauri, the closest known star to the Sun, is about 4.24 light-years away. That means its light takes roughly 4.24 years to reach Earth, so telescopes see it as it was in the past.

A common mix-up is confusing a light-year with a measure of time because it contains the word “year.” Professional astronomers often prefer the parsec: one parsec is approximately 3.26 light-years. The International Astronomical Union formally defined the modern light-year using the Julian year and the exact speed of light.