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Superluminal motion refers to faster-than-light (FTL) motion, a term used in astronomy for discussing observations that appear to indicate such motion. An example of such apparent superluminal motion is that of knots (fat parts) in AGN jets (as per radio observations), which observations over time sometimes show to be moving across the celestial sphere at a rate, which, with the determined distance to the galaxy, indicate the knot is moving faster than the speed of light (c). The general explanation is that the jet is relativistic and rather than being beamed within the plane of the sky, is beamed toward Earth with a small angle between the jet and our line of sight, and as time passes, EMR reaching us from the knot has traveled a shorter distance than earlier. With some specific geometry, the motion taken as across the sky appears faster than c. Some observations have suggested some of the jet angles don't fit with this explanation, so possibly there is more to it, though actual "faster than light" travel is not considered a reasonable explanation.
If two observable events are equally distant from us and we know that distance, by simple triangulation we can work out the "speed of something" by which the one event triggered the other. This "speed of something" could any speed up to the speed of light, e.g., ultrarelativistic. If the second event is actually nearer to us rather than equally distant, a corner has been cut off the sequence of two routes, i.e., the route from one event to the other followed by the route of the second event's light toward us. We see the second event earlier than would be possible if the second event were actually equally distant from us.