That's our acceleration as a function of time. Let's say we don't know the velocity expressions, but we know the velocity at a particular time, and we don't know the position expressions, but we know the position at a particular time. Let's say we know that the velocity at time 3, let's say 3 seconds, is negative 3 meters per second. Actually, I'm going to write the units here and make it a little bit. This is meters per second squared. That's going to be our unit for acceleration. This is our unit for velocity.