What are static and dynamic stretching?

In one line

Static stretching holds a muscle still in a lengthened position, while dynamic stretching lengthens muscles by moving a joint again and again.

What are static and dynamic stretching?
Stretching while still vs. stretching while moving
Before or after a workout, some people hold a straight leg in a long stretch, while others swing their legs back and forth. Both are stretching, but they have different names. This post explains what static and dynamic stretching are, how they differ, and what changes in the body afterward.
In one line
Hold still and it is static; keep moving and it is dynamic
Static stretching means holding a muscle in a lengthened position without moving for a while. Dynamic stretching means moving the arms or legs again and again so the muscle lengthens and relaxes. 'Static' means staying still; 'dynamic' means moving.
What stretching is
Moves that lengthen a muscle
Stretching is straightening or bending the trunk, arms, and legs to lengthen muscles. The goal is to widen the range a joint moves from one end to the other, called the 'range of motion'. Static and dynamic are names for different ways of doing it.
Static stretching
Lengthen, then hold still
In static stretching, you lengthen a muscle until you feel a pull or mild discomfort, then hold that position for a set time. An example is sitting on the floor with straight legs and leaning forward, holding the hamstrings at the back of the thigh in a lengthened position.
Dynamic stretching
Lengthen and release while moving, over and over
Dynamic stretching does not stop in one position; it moves a joint again and again, under control, within its range. An example is the 'leg swing', standing and swinging one leg forward and back. Each time the leg comes up in front, the hamstrings lengthen and then relax.
Ballistic stretching
Bouncing at the end has its own name
Moving faster than in dynamic stretching and bouncing at the end where the muscle is most lengthened is called 'ballistic stretching'. Researchers see it as a faster form of dynamic stretching.
Right afterward
All three methods widened range of motion
One session of stretching widened range of motion right away. The gain was small, and there was no difference between static, dynamic, and ballistic methods. There was also no difference by how hard people stretched or whether they usually exercised.
Where each is commonly used
Dynamic before workouts, static for regular stretching
Dynamic stretching is often included in the warm-up before exercise. A warm-up is light exercise that heats up and prepares the body before the main workout. Static stretching is the most common method in regular stretching programs done over several weeks to widen range of motion.
Common myth
Does stretching make muscles longer?
Many people think stretching lengthens the muscle itself. But the wider range of motion after one session or a few weeks of stretching came mainly from getting better at tolerating the pulling feeling. Changes in the length of the muscle itself were very small and appeared only with a lot of hard stretching.
Summary
Still is static, moving is dynamic
Static stretching holds a muscle in a lengthened position; dynamic stretching lengthens muscles by moving a joint over and over. The wider range of motion after stretching comes more from tolerating the pull better than from muscles getting longer. Related terms: range of motion, warm-up, foam roller.