Bug Life Cycle:

Any abnormality in software is known as Bug. Or If
application do not match with the requirements, it is
reported as Bug. The elimination of bugs from the
application depends upon the efficiency of testing done on it.
Bug also follows a life Cycle as SDLC.
From initial stage when a new defect/bug is logged in Bug
Tracker (Bug Zilla, Quality Center etc), it is in open state
and when it is corrected, it is said to be closed.

The different stages of a bug is as follows:
1. New
2. Open
3. Assign
4. Test
5. Verified
6. Deferred
7. Reopened
8. Duplicate
9. Rejected and
10. Closed
Description of Stages:
1. New: When the bug is logged for the first time, its stage
is known as “NEW”. This means that the bug is not yet
approved/validated.

2. Open: After a tester has logged a bug, the lead of the
tester approves that the bug is valid and he changes the
state as “OPEN”. (Depends upon Company's way of working,
Tester can also change the status to "Open").

3. Assign: Once the Test lead validates the bug as “OPEN”,
he assigns the bug to corresponding developer or developer
team. At this stage bug status is changed to “ASSIGN”.

4. Test: Once the developer fixes and corrects the bug, he
has to assign the bug to the testing team for next round of
testing. Before he releases the software with bug fixed, he
changes the state of bug to “TEST”. It ensures that the bug
has been fixed and is again released for testing to the
testing team. 

5. Deferred: The bug, changed to deferred state means the
bug is expected to be fixed in next releases. The reasons
for changing the bug to this status have many factors. Some
of them are priority of the bug may be low, lack of time for
the release, bug cannot be fixed due to architecture reasons
or the bug may not have major effect on the software.

6. Rejected: If the developer replicates the bug, and
results are not same, he can reject the bug. And the status
is changed to “REJECTED”.

7. Duplicate: If the bug is repeated twice or the two bugs
mention the same concept/scenario of replication, then one
of the bug status is changed to “DUPLICATE”.

8. Verified: Once the bug is fixed and the status is changed
to “TEST”, the tester tests the bug. If the bug is not
present in the software and is fixed properly keeping in
mind other functionality is unharmed due to fixation of
defect, he approves that the bug is fixed and changes the
status to “VERIFIED”.

9. Reopened: If the bug still exists even after the bug is
fixed by the developer or after fixing the defect it is
creating problems in other part of application, the tester
changes the status to “REOPENED”. The bug again follows the
same life cycle once again.

10. Closed: Once the bug is fixed, it is tested by the
tester. Tester validates that the bug no longer exists in
the software, and changes the status of the bug to “CLOSED”.
At this stage, bug is fixed, tested and approved.

Also, there are 2 more terms associated with Bug life Cycle.
These are Priority  and severity of defect.

Severity is defined as the impact of defect on the
application and Priority of defect is categorized into 4
different phases:

Critical / Show Stopper — This type of defect prevents
further testing of the product or function under test, and
is classified as Critical Bug. Examples of this include a
missing menu option or VB script errors or security
permission required to access a function under test or
Broken Links etc. Work cannot be continued on the application.

Major / High — A defect that does not function as projected
for or causes other functionality(ies) to fail to meet
requirements is categorized as Major Bug. Examples of this
include inaccurate calculations; the wrong field being
updated, frames of the application giving error or Links
navigate to wrong pages etc. Work  (work around)can be
continued with the occurrence of this defect.

Average / Medium — These defects do not conform to standards
and conventions are categorized as Medium Bugs.  Examples
include matching visual, fonts and text links which lead to
different end points. Workaround can be continued to achieve
functionality objectives.

Minor / Low — These defects are also called as Cosmetic
defects. These defects does not affect the functionality of
the system and are classified as Minor Bugs. 
Continuous testing of an application can be done and these
defects are fixed at the end of build. Examples: Spelling
errors in descriptions of text boxes, etc.

After Confirming it as a bug,you have to post it in to bug
tracking tool.Then the status of bug will be "NEW".Our Team
lead or any senior person will review it and if it is really
a bug, then he/she will change the status to "OPEN".if
he/she confirms that is not a bug and change the status to
"CLOSED".

All the Open Status Bugs send to the developer team.there
team lead will assign the bug to corresponding
developer.he/she change the status to "ASSIGN" and add the
corresponding developer name.when developer fix that
bug,he/she changes the bug status to "TEST".

If the development team lead confirmed that this is not a
bug, then he rejects that bug with valid reasons.Then the
status of that bug will be "REJECTED".

If he/she confirmed that this is not required for the
current build, but may be useful for the future
releases,Then he change the status of bug as"DEFERRED".All
the deferred bugs will be considered for future releases.

All the test status bugs will be mail to testing team. the
corresponding tester test that bug in new build or patch and
change the status as "CLOSED" If it is fixed otherwise to
"RE-OPEN" if it is not fixed.

All the reopen bugs will be mailed to the development team
and then the above cycle repeats.