The crossword solution for the term 'Where the Mouth Is' is DELTA. DELTA is a Greek letter that is often used to represent change or difference in mathematics and science. It is also used to refer to the fourth letter of the Greek alphabet, which is pronounced 'dahlta'. In the phrase 'Where the Mouth Is', it is used to mean that one should put their money where their mouth is, meaning that they should back up their words with action.