The term "rate change velocity" is not a standard scientific or mathematical term. It's possible that it's being used in a specific context, and understanding that context would be necessary to give a precise definition.

However, based on the words, we can infer what it might mean:

* Rate of change: This usually refers to how quickly something is changing over time. It can be calculated by finding the difference in the value of a quantity over a specific time interval and dividing that difference by the time interval.

* Velocity: This is a vector quantity that describes both the speed and direction of an object's motion.

Therefore, "rate change velocity" could potentially refer to:

1. The rate of change of velocity: This is called acceleration, which is a measure of how quickly the velocity of an object is changing. It's a vector quantity and can be positive (speeding up), negative (slowing down), or zero (constant velocity).

2. The change in velocity over a specific rate: This could be interpreted as calculating the difference in velocity over a particular time interval, which again, is related to acceleration.

Without further context, it's difficult to provide a definitive definition of "rate change velocity."

If you can provide more information about where you encountered this term, I might be able to give you a more specific answer.