what is defect life cycle?

The defect life cycle is:
first when the defect is found it is made note of. (this is called the New stage)
Then it is sent to the developer (this is called the Open stage)
Once the developer fixes and sends back to the tester (it is called as Fixed)
Now the tester checks if the bug had been fixed , if it is fixed (it is called Closed)

if the bug is not fixed it is returned back to the developer (this is called as Reopen)