Definitions
1.AdjectiveOf a four-vector in representing a point in spacetime, having a positive or negative four-vector norm for the metric signature (+, -, -, -) and (-, +, +, +) respectively.
2.Adjective(of the interval between two events in spacetime) Having overlapping light cones, so that information can pass from one to the other, and one can be envisaged as a cause of the other.