Okay, just looked up velocity and vector. I learned way back in school that direction was trajectory. Velocity is speed. The physics definition is enlightening. Still, that is only 2 dimensions. Where is the 3rd? BTW, that is not what most people believe about velocity and trajectory. Guess we're all behind the definitions.
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’.