What is Bug Life Cycle.

I would describe this as below:
A Tester finds a defect and logs it. (But before you log it, you must try to recreate it for 3 or 4 times so that you are 100% sure that it is a bug)
The defect is now approved or disapproved by the Test Lead.
(If it is disapproved, then the test lead will come to you ask for more details and you have explain to him why it is a bug)
After the Test Lead approves the bug, it is now assigned to a development Team Lead (or Development Manager). He/she now assigns that bug to the concerned developer. The developer now looks into the bug and fixes it. Once the fix is ready, there will be another build ready to test. The tester now tests the defect. It the defect is fixed, then the tester closes the defect, if not then the test will reopen it and same cycle starts.