A hideout is a secret place where someone can take refuge. Criminals or outlaws often lie low in a hideout to avoid being found by the police.
A car thief might use his grandmother's apartment as a hideout to avoid detection. A group of ten year-olds might also have a hideout, a place that's protected from parents, bullies, older siblings, and anyone else who might interfere. Before the first use of hideout, in the 1880s, came the verb phrase hide out, or "hide from authorities," which was coined during the Civil War in reference to draft dodgers.