Velocity is found by dividing the total amount of space an object moved by a measurement of time and combining that with the direction it moved. Velocity is a vector, and speed is only part of this vector.
In scientific areas, velocity is generally measured in meters per second. However miles per hour is common in many parts of the world as well when discussing an object's speed. When dealing with answers for scientific questions, it's important that the direction of motion is noted. However, questions that call for the "scalar velocity" do not require dealing with the direction component.