The Politics of India works within the framework of the country’s constitution. India is a parliamentary secular democratic republic in which the President of India is the head of state and the Prime Minister of India is the head of government.
Political parties and alliances in India: The two main parties in India are the Bharatiya Janata Party (BJP led NDA), also known as the NDA, which is the leading right-wing party, and the Indian National Congress, commonly called the INC or Congress, which is the leading centre-left leaning party (UPA – United Progressive Alliance). Many spin-offs like TMC (Trimol Congress from Congress), and regional parties like DMK, Shiv Sena, JDU, RJD, LJP, SP, etc. along with newly emerging parties like Aam Aadmi Party (AAP), Hindustani Awam Morcha (HUM), etc. are political contributors in India.
Defection in terms of politics: It is defined as either voluntarily giving up the membership of his party or disobeying (abstaining or voting against) the directives (political whip) of the party leadership on a vote in legislature.
The anti-defection law in India, technically the Tenth Schedule to the Indian Constitution, was enacted to address the perceived problem of instability caused by democratically elected legislators in India’s Parliamentary System of Government shifting allegiance from the parties they supported at the time of election, or disobeying their parties’ decisions at critical times such as during voting on an important resolution. Such shifting of allegiance was considered to be a symptom of endemic political corruption, which in turn provided some legitimisation for corruption prevalent in other aspects of life in the country. (Partially sourced from Wikipedia)