Winter Session is the session of Parliament that is convened from November to December for a period of 3 weeks. It marks the end of the Parliamentary year. It follows the Monsoon Session which is also 3 weeks long and convened between July and August. The longest session is the Budget Session between January and April or May. Indian parliament does not have a fixed parliamentary calendar and the 3 sessions are a convention. The power to convene a session is with the government and the summoning is by the President.