Need some light shedding on this strange term?  Here are some definitions.

From Parliament’s own website:
https://www.parliament.uk/site-information/glossary/prorogation/

Prorogation marks the end of a parliamentary session.  It is the formal name given to the period between the end of a session of Parliament and the State Opening of Parliament that begins the next session.  The parliamentary session may also be prorogued when Parliament is dissolved and a general election called.

How is prorogation marked?

The Queen formally prorogues Parliament on the advice of the Privy Council.

Prorogation usually takes the form of an announcement, on behalf of the Queen, read in the House of Lords.  As with the State Opening, it is made to both Houses and the Speaker of the House of Commons and MPs attend the Lords Chamber to listen to the speech.

The same announcement is then read out by the Speaker in the Commons.  Following this both the House of Commons and House of Lords are officially prorogued and will not meet again until the State Opening of Parliament.

Prorogation announcement

The prorogation announcement sets out the major Bills which have been passed during that session and also describes other measures which have been taken by the Government.

Prorogation: what happens to Bills still in progress?

Prorogation brings to an end nearly all parliamentary business.

However, Public Bills may be carried over from one session to the next, subject to agreement.  The first Bill to be treated in this way was the Financial Services and Markets Bill in session 1998-99.

From the BBC’s Politics pages:
http://news.bbc.co.uk/1/hi/uk_politics/a-z_of_parliament/default.stm

When a parliamentary session comes to an end, Parliament is said to “prorogue” until the next session begins.

Following the prorogation ceremony all outstanding business falls, including early day motions and questions which have not been answered.

Any uncompleted bills have to be re-introduced afresh in the next session.

The power to prorogue Parliament lies with the Queen, who does so on the advice of the Privy Council.

The ceremony

In an echo of the state opening of Parliament, the Speaker and members of the Commons attend the upper chamber where they listen to a speech by the leader of the House of Lords reviewing the session’s work.

By ancient tradition, legislation which has passed all parliamentary stages is given royal assent in Norman French using the words “La Reyne le veult”, which roughly translates as “the Queen wills it”.

The Speaker then returns to the Commons and reads out the same speech.

Following this, the House is officially prorogued and the Commons will not meet again until the next state opening of Parliament.

There’s also some more useful stuff in
House of Commons Factsheet P4 “Sittings of the House” at: 
http://www.parliament.uk/documents/upload/p04.pdf

and you can view the most recent prorogation at https://www.parliament.uk/about/how/occasions/prorogation/