What is the difference between pressed and lose eyeshadow?

A pressed eyeshadow is one that is usually in a pan. It is a specific shape and is very compact. If you flip it upside-down, technically it shouldn't flake off.

A loose eyeshadow is usually in a jar or a baggie. They are literally a loose powder. Kinda like sand except smoother. If you flip it upside down, it will all fall out. Loose eye shadows tend to either be mineral or pigments and can be used wet by adding a little water to be more intense. They tend to come from indie brands too. Hope this helps!