The noun retreat means a place you can go to be alone, to get away from it all. A spot under a shady tree might be your favorite retreat from the sun, or your bedroom in the basement may serve as a retreat from your siblings.
In the military sense, the noun retreat means the withdrawal of troops. The British retreat after the Battles of Lexington and Concord gave the American colonists an early taste of victory during the American Revolution. As a verb, retreat means to back out of something — like a lawyer who is forced to retreat from his argument when the opposing evidence is too convincing.