lightyear

This term is frequently misunderstood by laypeople as a measure of time due to the presence of the word year. However, it is strictly a unit of distance used in astronomy to describe the vast gaps between stars and galaxies.

In technical writing, it is often written as two words (light year), though the single-word form is standard in scientific contexts. Because it represents a fixed physical constant, it is used exclusively for interstellar or intergalactic scales and is never applied to terrestrial distances.