We have multiple joints that all move in incredibly unique ways. Simple terms like up, down and sideways don't apply here, We need unique terms to describe unique motions, and when we are talking about anatomical motion, we reference an imaginary body, in something called "the anatomical position".
We must first start with a reference:
The anatomical position.
- Standing upright
- Feet forward
- Arms by your side
- Palms forward
- Head neutral looking forward
Always refer to the anatomical position whenever you discuss types of joint/body movement. This is your starting position whenever you are talking about direction or motion.