The main difference between speed and velocity involves

a. gravity.

b. direction.

c. distance.

d. weight

B. Direction

Velocity of a body involves magnitude and direction. So it would be meaningless to describe velocity without direction. It's a vector quantity

Speed of a body is the distance covered by it in unit time. It only involves magnitude of a body. It's a scalar quantity.

Velocity is a speed and the direction in which it's speeding.

The main difference between speed and velocity is direction.