Regression VS Retesting

Regression testing:-

Regression testing is a style of testing that focuses on retesting after changes are made. In traditional regression testing, we reuse the same tests (the regression tests). In risk-oriented regression testing, we test the same areas as before, but we use different (increasingly complex) tests.

Regression testing attempts to mitigate two risks:
• A change that was intended to fix a bug failed.
• Some change had a side effect, unfixing an old bug or introducing a new bug.
The essence of regression testing is exposure of problems that shouldn't be there, either because they were exterminated before or they weren't in the product the last time(s) it was tested.

Retesting
Retesting is a measurement or control process, a means of assuring that the program is as stable as it was previously.

For regression testing we execute the failed test cases (also updated and added testcases) and for retesting we use to execute passed testcases. So

Regression:- 10 testcases
Retesting:- 90 testcases.