A machinery shell is an enclosure built around a piece or a cluster of machinery, which functions more as a container for the equipment inside than as a regular building. The interiors of these structures generally have very limited or no accessibility to humans. Instances include some electrical substations, utility distribution units, and junction boxes.

The enclosure primarily contains equipment and provides little or no regular interior space for people. It differs from a building arranged for accessible working or occupied areas.

A single machine or a group of machines can be enclosed. The shell provides containment, while an exposed machine structure has its machinery integrated directly into its visible form.