The term 'BUSINESS UPPER' can be broken down into two crossword solutions, 'BOOM' and '4 letters'. The term 'BOOM' is often used to describe a sudden increase in activity or success, which is often associated with business. The term '4 letters' refers to the fact that the word 'BOOM' is composed of four letters. Therefore, the term 'BUSINESS UPPER' can be interpreted as a sudden increase in business success.