An enclosure is something that surrounds and contains a space or keeps things inside. A zoo enclosure is the fenced or walled area where animals live. A backyard enclosure might keep your dog safely contained while letting them run around. An envelope is an enclosure for a letter.

The word suggests a boundary that creates a separate, protected, or controlled space. A playground enclosure has fences that keep children safely inside the play area. Scientists might study mice in laboratory enclosures where they can carefully observe behavior. Even a fortress wall creates an enclosure that protects the people inside.

In history, the Enclosures refers to a period in England (mainly the 1700s-1800s) when wealthy landowners fenced off land that farmers had shared for centuries. Before enclosure, villagers could graze their animals and grow crops on common land. After enclosure, those same fields became private property surrounded by fences and hedges. This forced many farming families to move to cities to find work, fundamentally changing English society.

When writing a letter, people sometimes say “see enclosure” to mean “look at the extra document I've included.” An enclosed space feels shut in or surrounded, like an enclosed porch with windows and walls on all sides.