Can someone explain what average velocity is? I know that it's change in position/change in time = $\displaystyle \frac{\Delta s}{\Delta t}=\frac{f(t+\Delta t)-f(t)}{\Delta t}=v_\text{avg}$, but exactly does this mean. Also, how is this different from instantaneous velocity? How is this different from a body's velocity at an exact instant?

Thanks in advance!