Dynamic stretching is a method of increasing a range of motion through movement and engaging your muscles so that they are prepared to work. Typically you wont hold a given position for any longer than 5 seconds before moving into a new position or adjusting the intensity of the stretch. This allows dynamic mobility work to be ideal right before a workout without taking any power away from the muscle.
Watch the video below for an example of a dynamic stretch. Note that you could hold the stretch position for longer for it to become a static stretch.