While many people think of the sand-filled playground when they are confronted with the term "sandbox" calculating a sandbox is a practical tool that serves as a container in which the user can execute code, make modifications, and otherwise interact with software without compromising the larger computer system.
Sandboxing can be simple, such as the sandbox desktop software, which creates simple sandboxes for individual programs or is so complex that multiple physical servers can be integrated. Sandboxing gives people the ability to execute code and experiments without making permanent (and potentially harmful) changes to the system in which they work.
A simple example of how a home user could use a sandbox would be to run your web browser in sandboxed formats when you visit suspicious sites or start an application from a source that you do not fully trust. In both cases, the activities of the web browser and the application launch would be in the sandbox, and malicious changes would fail reach the primary operating system (and would be discarded completely when the sandbox is stopped).