Which term defines how fast you are going in a specific direction?

The term that defines how fast you are going in a specific direction is velocity. Velocity is a vector quantity, meaning it has both magnitude (the speed) and direction. This distinction is crucial because speed alone only tells you how fast an object is moving, without any information regarding the direction of movement.

For example, if a car is traveling at 60 kilometers per hour to the north, this specifies its velocity due to the inclusion of direction. In contrast, when someone simply states that the car is traveling at 60 kilometers per hour, that describes the speed but does not provide the directional context that is necessary to fully understand its motion.

The other terms—momentum, speed, and acceleration—do not completely capture the concept of motion with direction like velocity does. Momentum relates to mass and velocity together, speed offers only the measure of distance over time, and acceleration describes the rate of change of velocity.