The Western Front refers to the fighting that took place in France and Belgium.
The German war plan - the Schlieffen Plan - involved invading France by going through Belgium.
Fighting on the Western Front started in 1914 when Germany invaded Belgium and France. It lasted until the armistice in November 1918.
When we talk about the armies on the Western Front we often just refer to the German, French, British, Belgian and, from 1917, American armies. However the British Army in particular included many different nationalities from all over the British Empire, including Australian, Canadian, New Zealand and Indian soldiers. The French Army also included soldiers from their African colonies.
The fighting on the Western Front left Belgium and France totally devastated. Whole villages and towns disappeared, smashed to pieces by the huge artillery guns used by both sides. Thousands of people became refugees. This had a big impact on France's approach to peace talks after the war - they wanted to punish Germany for the damage done to their country.
After the war, the Austro-Hungarian Empire was broken up and in the Treaty of Versailles Germany lost large areas of territory and had to pay reparations. This humiliation was a key factor in the radical politics that emerged in Germany over the coming decades.