The measure of speed in a certain direction is called velocity.

Here's the breakdown:

* Speed: How fast something is moving. It only tells you the magnitude (how much).

* Velocity: How fast something is moving *and* in what direction. It tells you both magnitude and direction.

Example:

* A car traveling at 60 mph has a speed of 60 mph.

* A car traveling at 60 mph east has a velocity of 60 mph east.