Diversion of income means to divert income to other person(s) under a pre-existing title.
Suppose A & B are Co-owners of a house which is given on Rent to C for10000/ pm.
Now C issues a cheque for Rent payment for one month to A of10000/-, even though A is entitled for only5000/-. He has to give5000/- to B. So, in this case it can be said that A has to divert5000/ to B. The amount taxable in the hands of A will be only5000/-.
Application of Income: ---------------------- Now out of10000/ diversion of5000/ has been made to B. The amount left with A is his own income. He wants to give you a party and spends1000/- on it. This will be called application of income. As the income of Rs.5000/- has been once taxed so application of income will also not be taxable.