Regression testing is a crucial part of software testing that ensures that changes made to an application do not introduce new defects or issues into a previously working functionality.

In other words, regression testing is the process of testing existing features of a software application to ensure that they continue to function as expected after new changes or updates are made.

Regression testing is performed to identify potential issues that may arise as a result of changes made to the software application.

For example, if a software developer fixes a bug in one part of an application, it is possible that the fix could have unintended consequences in another part of the application.

Regression testing helps to ensure that any such issues are caught and resolved before they can affect end-users. Regression testing can be performed manually or with the help of automation tools. Manual testing involves testers manually executing test cases that cover all the functionalities of the software. This can be a time-consuming process, but it can be effective for small software applications with a limited number of features.

Automation testing, on the other hand, involves using automated tools to execute test cases. This is faster and more efficient than manual testing, and can help identify issues that might be difficult for a human tester to identify.

In conclusion, regression testing is an important part of software testing that helps to ensure the quality of software applications. It is performed to identify potential issues that may arise as a result of changes made to the application, and can be performed manually or with the help of automation tools. By catching issues early, regression testing can help to improve the overall quality of the software and prevent expensive and time-consuming issues from arising later on.