The ratio of distance travelled to elapsed time — it tells you how fast, on average, the body was moving.
Symbols
v
average velocity
[m/s]
Δs
distance travelled
[m]
Δt
time
[s]
Where it comes from
Average velocity spreads the whole distance over the whole time — it says nothing about how the speed changed along the way. It is the ratio of the **total** distance travelled to the **total** time, not the average of the instantaneous speeds.
When to use it
When you know the distance travelled and the time, and the details of the motion do not matter. Note: if the body turns back, Δs is the length of the path, not the displacement.
Example
A car travelled 150 km in 2 h. Find its average velocity.