lightlike
Adjective
Meaning
lightlike (comparative more lightlike, superlative most lightlike)
(mathematics) (of a four-vector) Having a space component whose magnitude is equal to its time component multiplied by the speed of light.
Examples
Spacetime can be explored by following up on timelike and lightlike geodesics—all possible ways that light and particles in free fall can travel.
The first equation (or the second restricted to lightlike separation) leads to a yet larger group, the conformal group of spacetime.