English Constitution leaves the entire system of Cabinet to convention, the Crown being legally vested with absolute powers and Ministers being in theory nothing more than the servants of the Crown. Indian Constitution didn’t mention about it originally, but inserted by 44th Amendment in Article 352.
Cabinet is an extra-constitutional body based upon conventions.
It is the supreme policy making, highest decision-making & supreme executive body of the central government.
It is the chief coordinator of central administration.
It is an advisory body to the President and its advice is binding on him.
It is the Chief crisis manager.
It deals with all major legislative & financial matters.
It exercises control over higher appointments like constitutional authorities and senior Secretariat administrators.
It deals with all foreign policies.
The budget is, however, kept outside the purview of the cabinet. It is the exclusive domain of the PM and the Finance Minister and is revealed to the cabinet only a few minutes before it is presented to the Parliament.
The work of Cabinet is largely handled by Cabinet Committees.
Kitchen Cabinet/ Inner Cabinet: an extra-constitutional body consisting of PM and 2-4 influential colleagues in whom he has faith and with whom he can discuss every problem. It may consist of outsiders also like family & friends. Also exists in US & Britain.
Though an informal body, it is the real centre of power. Its main merit is its small size which enables more efficient & expeditious decision-making besides maintaining secrecy.