Test data refers to a set of predefined values or information that is used for testing and evaluating software applications, systems or components. It is often created by experts in order to simulate real-world scenarios and help developers identify any potential issues or bugs within their code before releasing it to the public. Test data can include various types of input such as numbers, text, dates, or even more complex values like lists, dictionaries or objects. The purpose of using test data is to ensure that software performs correctly under different conditions and meets its intended functionality, performance, security and reliability requirements.