Question

define average speed.

Answer 1

The total distance travelled by a body in a definite interval of time is known as average speed.
mathematically avg. speed = (total distance/total time).

Answer 2

"Average speed:

The "total distance" traveled by a "body in a definite interval of time" is known as "average speed".

By derivation it is represented as,

Average\quad speed=$(\frac { Total\quad distance }{ Total\quad timetaken } )$.

Speed is a scalar quantity. So it does not have a unit. the "instantaneous speed" is the "limit of the average speed" as the "duration of the time interval" approaches zero."