What This Is' is a phrase that can be used to describe something that is not immediately obvious or known. The crossword solutions for this term are CLUE, SEEDENTRY, and SEVENTEENACROSS. CLUE is a four-letter word meaning 'a hint or suggestion as to the solution of a problem'. SEEDENTRY is a nine-letter word meaning 'the first step in a process'. SEVENTEENACROSS is a fifteen-letter word meaning 'an indication of the nature or essential qualities of something'. Together, these three words provide an explanation of the phrase 'What This Is'.