The term 'WHAT'S THE BIG ___?' can be answered with two four-letter words: 'IDEA' and 'DEAL'. The phrase 'What's the big IDEA?' is a common expression used to ask someone why they did something, usually something that is seen as wrong or inappropriate. The phrase 'What's the big DEAL?' is used to ask why something is so important or why it is being given so much attention. Both phrases are used to express surprise or disbelief.