They're pretty much the same thing but when you hear the word rate of change, your thinking of it more in the context of a word problem and interpreting what it means. So labels are pretty much the key difference.
So like slope is here is a random coordinate plane, here's random points or just tell me what the slope is whereas rate of change is like it's number of meters per minute or its number of miles per hour so rate of change means you're comparing two quantities but you have units or labels attached to it.
You're calculating it in the same way but when we say rate of change we're really being asked in the context what does it mean.
