I'll add "what you don't care if they understand." For example, let's take a roundhouse kick:
- If I'm teaching a 4-year-old on his first day of class, as long as he stays with his line, I honestly don't care what he does. I don't care if all he does is step, and doesn't even kick. If he steps when I say "go" and stops after one or a couple, doesn't run into the person in front of him, and doesn't stand still so he can get kicked by the person behind him, I'm happy.
- If I'm teaching a 10-year-old on their first day, or if I'm teaching a 4-year-old who's been there for a couple weeks, all I care is they understand that a roundhouse kick has a turn, compared to the front kick we just did which is straight. I don't care if they don't chamber, and are basically just swinging their leg (toes up) across their body at knee height. They've learned the vocabulary I want them to learn - front kick is straight out, roundhouse kick is across.
- If I'm teaching someone who is getting close to yellow belt, I want them to know how to bend their knee and point their foot in the right direction.
- Close to purple belt, I want them to have a proper chamber and snap motion, and know how to point their foot.
- Close to orange belt, how to land that roundhouse kick to prepare for combination.
- Close to green belt, how to recoil their leg instead of just falling back to their sparring stance
Now, for that very first bullet point, I would still demonstrate knee up -> turn -> snap kick -> recoil -> land. I would demonstrate it fully. But all I care is that he stays in his line.