Parliament Square, in central London, is a rather small exposed patch of grass and trees studded with a few statues of notable people, not all of whom are or were British. Statues include those of Winston Churchill, which was given a mohican of turf during a demonstration, and Abraham Lincoln.
Parliament Square get's its rather uninspiring name from the fact that it lies directly in front of the Palace of Westminster, site of the Houses of Parliament.
Protests often take place on Parliament Square, and marches often end there, so as to gather people in front of Parliament: though because of the position of the square policing is sometimes heavy and very visible.