Mock objects are simulated objects that mimic the behavior of real objects in controlled ways. They are commonly used in software testing to isolate specific components, allowing developers to test functionality without relying on external systems or dependencies. This helps ensure that tests are reliable and repeatable. By using mock objects, developers can focus on the interactions between components, verifying that they communicate correctly. This technique is particularly useful in unit testing, where the goal is to test individual parts of a program, such as methods or classes, without the complexity of the entire system.