Is instantaneous velocity the same as instantaneous rate of change?

Question

The equation for instantaneous velocity is the limit as h approaches 0 of (f(t+h)-f(t))/h when t=time. The equation for instantaneous rate of change is the limit as h approaches 0 of (f(a+h)-f(a))/h when a=x of a point. Say we have a word problem discussing the position function of a ball falling from a cliff. Its position function isf(x)=16t^2+100. Using the functions, both the velocity and instantaneous rate of change would be -40ft/sec at point (1 , 1.5). Is there any difference conceptually between the velocity and instantaneous rate of change? Is velocity simply instantaneous rate of change but in terms of time?