Unit tests are a type of software testing that focuses on verifying the smallest parts of an application, known as units. These units can be individual functions or methods within the code. The main goal of unit tests is to ensure that each unit performs as expected, helping developers catch bugs early in the development process. By running unit tests, developers can confirm that changes to the code do not introduce new errors. This practice promotes better code quality and maintainability, making it easier to identify issues and improve the overall reliability of the software.