Conversation so far:
which state was not officially a state at the beginning of the civil war
The border states during the Civil War were the slave states that didn't leave the Union, including Delaware, Kentucky, Maryland, Missouri, and West Virginia.
was tennessee a border state
Though Tennessee had officially seceded and West Tennessee and Middle Tennessee had voted overwhelmingly in favor of joining the Confederacy, East Tennessee in contrast was strongly pro-Union.

Question: why was the term used for these states
Self-contained rewrite: why was the term border states used for delaware, kentucky, maryland, missouri, and west virginia