Unrealised Rent- If any amount of rent is not capable of being realised, then such portion of rent shall not be included in computing the sctual rent received or receivable.
Arrears of Rent Received- The assessee may have sought enhancement of rent from the tenant and the same could be in dispute. Subsequently as and when the additional rent is realised the same is liable to tax as arrears of rent received.
In both the above cases, even if the assessee is not the owner of the house property, it is chargeable under the head Income from House Property.