Assessee Category

it is the same as building owner and the lessor who taken lease for 15 years....

in case 1 he is the owner
in case 2 he is not the owner but enjoys all the benefit like a owner
..

deemed assessee - if a person is taxable for the income earned by some other person , but actually such income earned by other person is belong to him ( eg. income transfered , asset transfered by first person to later to avoid higher tax ) then he would be known as deemed assessee .
assessee in default - if any assessee didn't follow the provisions of the act then he would be known as assessee in default .

@ sagarnain a more best example would be....if you deposit a sum of 30 lacs in your account then the interest income would be taxable in your hands there you are the assessee.....if you have transferred that amount to your son's name then also it will be taxable in ur hands because here your son is the assessee but you are the deemed assessee

Ashwin, why is my son an assessee in this example
To begin with, 30 lacs is my income & transferring it to my son should be considered application of money
I should be treated as an assessee, not a deemrd assessee