Regression testing is any type software testing that seeks to uncover new errors, or regressions, in existing functionality after changes have been made to a system such as functional enhancement, patches or configuration changes.
It is a type of software testing that intends to ensure that changes (enhancement or defects fixes) to the software have not adversely affected it.
The likelihood of any code change impacting functionalities that are not directly associated with the code is always there and it is essential that regression testing is conducted to make sure that fixing one thing has not broken another thing.
During regression testing new test cases are not created but previously crested test cases are re-executed.
Software Test Analyst 