A 3 dimensional velocity vector would be (speed in x direction, speed in y direction, speed in z direction), if the 3 spatial dimensions are (x,y,z).
More mathematically, instead of speed in x direction, you would say change of location in the x direction with respect to time.
So, velocity would be (dx/dt, dy/dt, dz/dt), where d essentially means ‘change in’.
To summarize, what they are saying as that they know not only your current position in space, they also know how fast you are moving in each of the 3 dimensions, x,y,z, where x is left to right, y is forward-backward, and z is up-down.
Still sounds like trajectory to me. Guess I don’t have the brain power to get it.