The term BACK MUSCLE refers to the muscles located in the back, which are responsible for providing support and movement to the spine. The two crossword solutions for this term are LAT (3 letters) and STRAIN (6 letters). LAT is an abbreviation for the latissimus dorsi muscle, which is a large, flat muscle located in the lower back. STRAIN is a term used to describe an injury or damage to the muscles caused by overuse or overexertion.