The term 'Oh, So That's It' can be represented by three different crossword solutions: AHA (3 letters), ISEE (4 letters), and ISEENOW (7 letters). AHA is an expression of surprise or realization, often used when one has figured out a solution to a problem. ISEE is an acronym for 'I See', which is a phrase used to indicate understanding. ISEENOW is an expression of understanding, often used when one has just realized something.