What is the origin of the idiom "the whole nine yards" and when to use it?

The idiom "the whole nine yards" may have originated from the length of a machine gun ammunition belt during World War II, while others suggest it could be related to the length of fabric needed for a complete three-piece suit. Despite the uncertainty, it has become a widely used idiom in the English language. People use this idiomatic phrase to mean the entirety or full extent of something. It is often used to emphasize that everything possible or available is being included or considered.