A single congressional session lasts two years, for the duration of the Congress's tenure. Each congressional session is broken into two annual sessions that convene in January and continue until they are adjourned, usually towards the end of the calendar year. The president and leaders in Congress may also call special sessions of Congress as needed to deal with extraordinary circumstances.
Daily Sessions and Legislative Days
The term "session" is also used to refer to the days on which Congress actually meets. A "day of session" generally refers to an actual calendar day in which the legislative bodies meet. The number of days of session in a two-year congressional term can vary considerably, depending on the business each Congress deals with.