* Speed is a scalar quantity: It tells you how fast something is moving.
* Velocity is a vector quantity: It tells you how fast something is moving *and* in what direction.
Think of it this way:
* You drive your car at 60 mph. That's your speed.
* You drive your car at 60 mph *north*. That's your velocity.
To get velocity from speed, you need to add a direction.
Example:
* Speed: 25 m/s
* Velocity: 25 m/s east
In short, speed is a part of velocity, but you need more information (direction) to define velocity completely.
