The short answer is that velocity is the speed with a direction, while speed does not have a direction.

Speed is a scalar quantity—it is the magnitude of the velocity. Speed is measured in units of distance divided by time (e.g., miles per hour, feet per second, meters per second, etc.).

Velocity is a vector quantity—when giving the velocity we must specify the magnitude (the speed) and the direction of travel. For example you might drive 100km/hr (the speed) in a northerly direction.

This is analogous to the difference between distance (a scalar quantity) and displacement (the distance with direction).

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Sometimes it helps to have a visual representation:

This is a great question and I can see your confusion. There are similarities, but there are also differences. I will give you a definition of each and then provide an example.

Speed refers to how fast an object is moving. It is calculated by the displacement of space per a unit of time.

Velocity refer to the rate at which an object changes position in a certain direction. It is calculated by the displacement of space per a unit of time in a certain direction.

These definition might sound the same, but there is a crucial difference. It deals with direction. Velocity deals with direction and speed does not. Let me give you an example.

If you were driving at 50 miles per hour to get to a store, you would say that your speed is 50 miles per hours. If you were driving in a circle and ended at the same place, you would say that your velocity is zero, because there was no directional gain. The key to remember is that velocity is a vector, which means there is a directional component.

Speed is the ratio of distance traveled to the time elapsed.

i.e. speed = distance/time

whereas, velocity is the ratio of displacement to the time elapsed.

i.e., velocity = displacement/time

Now, displacement can be 0, but distance traveled cannot be. Think about what happens when we throw a ball up in the air and it falls down. It has certainly traveled certain distance; however its displacement (difference between initial and final position) is zero (as the ball started from ground level and came back to it). Thus, in this case, velocity is zero, speed is not.

Also, speed is a scalar quantity, i.e. it only has magnitude. On the other hand, velocity is a vector quantity, since it has both the magnitude and direction.

Both of them are measured in the same units of length per unit time.

Hope this helps.