A sandbox in testing is a controlled environment where software developers and testers can experiment without affecting the main system. It allows for safe testing of new features, bug fixes, or updates, ensuring that any issues can be identified and resolved before deployment. This isolation helps maintain the stability of the production environment. Sandboxes are commonly used in various fields, including software development, web development, and cybersecurity. They enable teams to simulate real-world scenarios and assess how applications behave under different conditions. This practice ultimately leads to more reliable and secure software products.