In simple words federal system can be defined as a kind of government into a country which has the separated power between the union or states.
For example states can control the police of there state, but not the army of the country,
While the army can be controlled by the union or centre, not by the state.
The Constitution of india has adopted the federal system which means, the power between the centre or states are separated,
In terms of the
1. Union list
2. States list
3. Concurrent list
Political scientists classified government into unitary and Federal on the basis of the nature of relations between the national government and the regional government. by definition, a unitary government is one in which all the powers are vested in the national government and the regional government, if at all exist, derive their authority from the national government. A Federal government on the other hand is one in which power are divided between the national government, and the regional governments by the constitution itself and both operate in their respective jurisdiction independently.
Britain, France, Japan, China, Italy, Belgium, Norway, Sweden, Spain and so on have the unitary model of government. while the US, Switzerland, Australia, Canada, Russia, Brazil, Argentina and so on have the federal model of government. in a federal model the national government is known as the Federal government or the central government for the union government and the regional government is known as the State government or the provincial government.