Let a rod be at rest in K', lying parallel to the x'-axis. Knowing the value of λ, we can say that:
(Theorem) The length of the rod contracts by a factor of √1 – v2 / c2 when viewed from K.
So the distance between the endpoints of the rod is different in K and K', or more generally, the distance that spatially separates two events (i.e. two entities at two given moments, respectively) depends on the inertial frame in which it is measured.
Note: length contraction is unnoticeable in our everyday life.