Section 119(2)(b) it act.

Central govt has delegated the power to CBDT grant relief by empowering the authorised officers to grant reliefs to the assessess which are unavailable due to time limitations.For eg if the ROI not filled within the due dates then he cannot carry forward the losses as per the strict provisions of sec 139 .But because if this section he can make application to those authorised officers for granting the releif by allowing to carry forward these losses to next AY .like this there are many reliefs allowed to assessee on the ground of reasonable causes to avoid genuine hardship and pave a way for govt to raise revenue rather than strict implementation of law in all cases ignoring genuine hardships faced usually by any common man in their life

It's for condonation of delay in filing of time barred --- ITR, Forms, TDS returns etc. The Assesee has to apply with genuine reasons to jurisdictional CIT for approval.