Two events that are simultaneous in one inertial frame of reference will not necessarily be simultaneous in any other inertial frame of reference. Explain.

Oh wow, this sounds like Relativity. I think it means when observing an phenomenon, it can be different. For example, when two cars are going 80mph on the highway. If you are in one of the cars and look at the other driver, it would seem that time has stopped for you and the other driver while the world moves.

While someone observing on the outside would see you two move while the world is still