A quick google search will help..
"Speed and velocity are both measured using the same units. The SI unit of distance and displacement is the meter. The SI unit of time is the second. The SI unit of speed and velocity is the ratio of two — the meter per second."
No it’s the same in physics and math. You’re confused because in the world of mor.onic stup.idity it’s slugs per in3.
Uhhhh...... a slug is a unit of MASS , not average velocity
so slug/in^3 would be a measure of density....
Velocity and average velocity are in the same units
Could be m/s or km/s or m/hr or ft/s etc (distance units) / (time units)