A light-year is defined as the distance travelled by light in a vacuum in one year. It is widely used in astronomy to measure stellar distances.

1. Definition: It represents the path length light traverses over a period of one year. Therefore, it is a unit of Length or Distance.
2. Value: According to NCERT Appendix A 4, 1 lightyear ($1 \text{ ly}$) = $9.461 \times 10^{15} \text{ m}$ .
3. Dimensional Analysis: Speed ($[LT^{-1}]$) $\times$ Time ($[T]$) = Distance ($[L]$).