Things that are enclosed are surrounded on all sides, closed or penned in. If your grandfather's condo development is enclosed by a high fence, you might need to check in with a guard before you can visit him.
Your pet guinea pig is enclosed by her cage, and when you're at school, you are enclosed by the walls of the building. Homes, car lots, gardens, and school yards are all commonly enclosed by fences. If you put a check inside your cousin's birthday card, the money is also enclosed. Enclosed comes from the verb enclose, which is rooted in the Old French enclore, "surround, confine, or contain."