What does "elbows in" and "elbows out" mean?
Why I couldn't find in the dictionary? Is this a short form?
When referring to parts of the body, usually “in” means closer to the body (or a line drawn from the center of your head straight to between your ankles) and “out” means further away.
For example, if you “tuck in” your chin, you draw it closer to your neck and chest. If you turn your palms “out”, they point away from your body.
If your elbows are “in” they’re closer to your torso. If they’re “out” they’re further away from your torso.