What is a federation?

The term ‘federation’ is derived from the Latin word foedus which means ‘treaty’ or ‘agreement’. Thus, a federation is a new state (political system) that is formed through a treaty or an agreement between the various units. The units of a federation are known by various names, like states (as in the US) or cantons (as in Switzerland) or provinces (as in Canada) or republics (as in Russia). 

Further Reading :

• Federal Features of Indian Constitution
• Challenges to the Federal Structure: RSTV – The Big Picture