Belly Trouble is a term used to describe abdominal pain or discomfort. It can be caused by a variety of conditions, such as indigestion, constipation, gas, and other digestive issues. The crossword solution for this term is ACHE, which is a four-letter word meaning a dull, continuous pain. ACHE can also refer to a feeling of distress or longing. In the context of Belly Trouble, it is used to describe the physical pain associated with digestive issues.