What is a plastic coin holder?

Excuse me, I was wondering if you could clarify something for me. I've come across the term 'plastic coin holder' and I'm not quite sure what it refers to. Could you possibly elaborate on what exactly a plastic coin holder is? Is it a type of container or case specifically designed to hold and protect coins, made from plastic materials? If so, what are some of the benefits or advantages of using such a holder? And are there different types or sizes of plastic coin holders available on the market to accommodate various coin sizes and collections?