A mural is a painting on a wall, ceiling, or other large permanent surface.
Murals of sorts date to prehistoric times such as the paintings on the Caves of Lascaux in southern France. There are many techniques. The most well known is probably "fresco", which uses water soluble paints with a damp lime wash, a rapid use of the resulting mixture over a large surface, and often in parts (but with a sense of the whole). The colors lighten when dried.
Murals today may be painted in a variety of ways, using oil or water based media. The styles can vary from abstract to Trompe L'Oeil (a French term for fool or trick the eye).
The most famous mural is probably Guernica, by Pablo Picasso. Picasso's painting commemorates a small Basque village bombed by The German Luftwaffe in April 1937 during the Spanish Civil War in support of Francisco Franco's Nationalist army. Picasso depicts a nightmarish scene of men, women, children and animals under bombardment. Art historian Herbert Read described the work as "a cry of outrage and horror amplified by a great genius".