In military terms, a salient is is a battlefield that is surrounded on several sides by enemy territory. There were five battles of Ypres. The first was in December 1914. The second ran from April to May 1915. The third (which was also known as the Battle of Passchendaele) was from July to November 1917. The fourth was in April 1918, and the fifth (also known as the Advance of Flanders) was from September to October 1918.
Ypres was known to the British troops as 'Wipers'.
Credit for this entry to: Alan Patient of www.plaquesoflondon.co.uk