The typical year by which the term of a Parliament is divided
The (usually) annual Parliamentary cycle, of which there will typically be several between General Elections.
Each Session is opened by the Sovereign (or, in exceptional circumstances, a representative of the Sovereign) in a ceremony called the 'State Opening of Parliament', where the Sovereign reads a speech outlining the legislation that Her Majesty's Government intends to introduce over the Session. Typically this occurs in June, though may vary due to the timing of General Elections.
The Session typically ends the following May with the prorogation of Parliament. Parliament is no longer in Session and cannot perform Parliamentary functions until the next State Opening.
No. If you assume that Parliament follows a typical school calendar, you'll be broadly correct.
Parliament will a long summer recesses, a 2 week recess each Christmas and Easter, and week recesses during half term. There is also a several week recess in September, when parties hold annual conferences. Except for the 13 days devoted to Private Members Bills, Parliament also does not sit on Fridays.
Parliament sits on around 170 of the c. 250 working days each year. MPs will stress that just because Parliament is not sitting, doesn't mean that MPs are not working, and most other national legislatures sit on even fewer days.
The Standing Orders of the House (the written rules of how Parliament operates) mandate a number of days be allocated to events during the year. Furthermore, there are conventions that expect a number of days debate for certain events that occur during the Session. The precise timing of the days not fixed by events are agreed between the party whips.
These pre-allocated days include:
The ending of the Session is called 'prorogation', and is announced by the Sovereign.
Sessions function as legislative 'gateposts' during the time of a Parliament. Any legislation that has not completed its passage by the prorogation of the Session is now removed from the list of active bills, with the exception of a few Government Bills that have applied for a 'carry over motion' that allows them to continue in the next Session.
The new Session starts with a clean slate for legislation, a new Queens Speech is delivered, new Private Members Bills may be tabled, and so on.