What is the difference between velocity & speed? What is velocity?

Velocity is speed for a specifc direction acceleration is increase in speed over time

Velocity is a vector quantity that refers to "the rate at which an object changes its position."

Acceleration, (symbol: a) is defined as the rate of change of velocity. It is thus a vector quantity with dimension length/time². In SI units, acceleration is measured in meters/second².

To accelerate an object is to change its velocity, which is accomplished by altering either its speed or direction (like in case of uniform circular motion) in relation to time. Acceleration can have positive and negative values. Any time that the sign (+ or -) of the acceleration is the same as the sign of the velocity, the object will speed up. If the signs are opposite, the object will slow down. Acceleration is a vector quantity. When either velocity or direction changes, there is acceleration (or deceleration).

Speed is a measure of time and distance, simply put.  It depends on how much time it takes an object to get from point A to B.  Velocity is a measure of speed that involves a direction as well, which makes it a vector.

Speed is a scalar quantity that measures magnitude, while velocity is a vector quantity that measures magnitude and direction.