Short answers, pulled from the story.
A light-year is a unit of distance equal to exactly 9,460,730,472,580.8 metres, or roughly 9.46 trillion kilometres and 5.88 trillion miles. It is defined by the International Astronomical Union as the distance light travels through a vacuum in one Julian year of 365.25 days.
A light-year is a unit of distance, not time. Despite the word "year" in its name, it measures how far light travels, not how long anything takes.
Otto Ule introduced the light-year unit in a German popular astronomical article in 1851. He compared it to the Wegstunde, a traditional unit describing how far a person walks in an hour, to explain the oddity of a distance unit named after a unit of time.
Professional astronomers most commonly use the parsec, which equals approximately 3.26 light-years. The parsec derives directly from parallax measurements, linking it naturally to the observational method used to gauge stellar distances. Light-years are used primarily in non-specialist contexts and popular science publications.
Before 1984, the IAU defined the light-year using the tropical year and a measured speed of light. From 1984 onward, the definition shifted to the Julian year of 365.25 days and the defined speed of light of 299,792,458 metres per second, both from the IAU (1976) System of Astronomical Constants.
MoM-z14, the farthest confirmed galaxy discovered as of 2025, is about 13.53 billion light-years away in light-travel distance and 33.8 billion light-years in proper distance. The comoving radius of the entire observable universe extends to about 45.7 billion light-years in any direction from Earth.