Identifying Bindings

What do we mean when we discuss a book's binding? 

When we look at a book's binding, what are we looking for? How do we discuss a binding?

Terminology: 

These terms are drawn from the ABC for Book Collectors, and the RBMS Controlled Vocabulary.

For Catalogers: 

For those catalogers using the MARC system, the RBMS Controlled Vocabulary site is an essential resource.