Define velocity and acceleration.

Hint: To define velocity and acceleration, we must know about the displacement and distance of the body from one position to another position. Also, the required time interval to complete the motion from initial to final position.

Complete step by step answer:
Let us define velocity first.
Velocity: The rate of change of the position or displacement of an object with time is called velocity of that object.
$\text{Velocity} = \dfrac{\text{Displacement}}{\text{Time}}$
Velocity is the vector quantity whose direction is given by the direction of force. The unit of velocity in the SI or MKS system is $m{s^{ - 1}}$ or $cm{s^{ - 1}}$. The velocity of an object is taken positive if the object is moving towards the right of the origin and negative if the object is moving towards the left of the origin.

Acceleration: The time rate of change of velocity of a body is called acceleration.
$\text{Acceleration} = \dfrac{{Velocity(\Delta v)}}{{time(\Delta t)}}$
If in a given time interval the velocity of a body changes from $u$ to $v$ , then acceleration $a$ is expressed as
$a = \dfrac{{v - u}}{t}$
Where, $v$ - final velocity and $u$ - initial velocity.
It is also a vector quantity having SI or MKS units is $m{s^{ - 2}}$or $cm{s^{ - 2}}$. Its direction is the same as that of change in velocity, but not of the velocity.

Note: Do not confuse speed and velocity. Speed is a scalar quantity which represents the total distance travelled per unit time and it is always positive, but velocity is vector quantity and is displacement per unit time and can be positive and negative both.