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