Confirmation testing is also known as re-testing.
Confirmation Testing is done to make sure that the tests cases which failed in last execution are passing after the defects against those failures are fixed.
For Example:
Suppose you were testing some software application and you found defects in some component.
1. You log a defect in bug tracking tool.
2. Developer will fix that defect and provide you with the official testable build.
3. You need to re-run the failed test cases to make sure that the previous failures are gone.
This is known as confirmation Testing or Re-testing