Complex sentence: Unifying the three spatial dimensions with time constructs the entity of four-dimensional pseudo-Euclidian spacetime called a Minkowski space, an interval in spacetime is invariant, an interval one of the four component dimensions is frame dependent.
Split into simpler sentences: Unifying the three spatial dimensions with time constructs the entity of four-dimension pseudo-Euclidian spacetime called a Minkowski space. An interval in Minkowski space is invariant, while an interval in one of the four component dimensions is frame dependent.