A Wendy house is a small structure built as a child's playhouse, usually placed in a garden or backyard of a home. These small structures can vary in features and size, though the general style is quite simple and small to accommodate children rather than adults. The first Wendy house models became available after a Wendy House was built in J.M. Barrie's play, Peter Pan, or the Boy Who Wouldn't Grow Up. A character in the story named Wendy is shot with an arrow, and a group of boys build the house around her to protect her. After the story became popular, so, too, did the child's structures.

The design of a Wendy house is fairly straightforward: a peaked roof covers a square footprint. The Wendy house may feature a small front porch, a front door, and sometimes even a front window. In some instances, the entire house is painted a bright color such as red or yellow. The house is built on a very small scale to be used as a playhouse rather than a more utilitarian structure, and the inside of the house can vary in size and style depending on the builder's preferences. Most simple Wendy house structures are bare inside, allowing the children to take toys inside or use their imaginations to construct a world within the house.

Variations on the house design have become prevalent as time has passed since the originals were built. Prefabricated plastic Wendy houses can be purchased and simply placed in the yard instead of being built as a solid and permanent structure. Other designs include Wendy houses built off the ground on stilts, with a stairway that leads up to a small porch; a more elaborate building with more than one room or a T-shaped footprint rather than a square or rectangle; and more elaborate porches, windows, and doors, as well as porch railings that feature planter boxes.

Some full-sized houses are even designed after the Wendy house design. These structures are often much larger and feature several rooms, and some even feature a second floor, though all preserve the general look and style of the smaller Wendy houses. Many homeowners have taken to building Wendy houses not for play, but instead for use as a garden shed or even as a workspace. These houses tend to be slightly larger than true Wendy houses to accommodate adults entering the structure.