A military ceremony generally including music, a ceremonial guard, and flags. The central part of the ceremony is the beating of the retreat, which includes a drummer's call. Traditionally, this was the call for all the soldiers to return to the fort after their evening liberty.
The tattoo ceremony often tends to include a sunset ceremony, which is the ceremonial lowering of the flags. Also, from its religious roots comes the evening hymn.
Sometimes, a tattoo can be more than a single ceremony. There are often displays of skill and competitions, sometimes among different units, but also between the military members and the civilians.