New: when tester reports a defect

Open: when developer accepts that it is a bug or if the developer rejects the defect, then the status is turned into "Rejected"

Fixed: when developer make changes to the code to rectify the bug...

Closed/Reopen: when tester tests it again. If the expected result shown up, it is turned into "Closed" and if the problem persists again, it's "Reopen".