Error is human made mistake
Defect is when this mistake is present in the component or
application.
Failure is the deviation from what the system is supposed to
do due to the presence of defect

Bug: Error which appears during testing phase

Defect: Error that appears during development phase

Failure: When the result is not equal to actual result then 
it is said to be Failure

Fault & Mistake: Errors which are made at that time and 
recognised at that time itself

Defect is the deviation from Requirements given by 
customer/client.(Black Box Testing)
Error is related to the development activities it may be 
synatctical or logical error.(White box testing)
Failure is the impact of error/defect on other features of 
program or application.(Black box testing)
Bug is the informal name given to defect(BBT)

1. Fault & Mistake: wrong coding done by Developers
2. Failure: When the result is not equal to actual result 
then it is said to be Failure
3. Error: Faults and Mismatches in Coding during testing is 
called Error
4. Defect: When Testengineer find that Errors called that 
Defect
5. When Developers Accepted that Defects then it is called 
Bug

Bug/Defect :

A bug or defect is a flaw in a system or system component 
which may cause the system or the system component fail to 
perform its desired action.

Error :
It is a human mistakes

Failure :
If the product or the application falied to perform its 
desired action according to end-uesr prospective.

Fault :
It is a incorrect intermediate statement encounter during 
program execution

Mistake :
Nothing but error raised by human action

Answer no six is good one

Nonu

BUG: A Bug is a Application Error, in Software doesn't
affect the whole application in terms of running.It doesn't
stop the execution of application.It produces wrong output.
                     OR
Anything that prevents the software program to perform   
its required function.
                     OR
Any thing that effects functionality.
                

Error : A mistake made by programmer.
                 OR
        Anything that stops the execution of application.

FAULT: An incorrect step, process, or data definition in a
computer program which prevents the program to perform an
intended or anticipated manner.

FAILURE: A failure occurs when a fault is executed.The
inability of a system or component to perform its required
functions within specified performance requirements.

DEFECT : If a problem occurs once the application is hanged
to the end user or client.

    we Can Say:
                Error >> Fault >> Failure >> Defect

all are relatively the same because all of them are caused due  
to the human carelessness.

error: A human action produce incorrect result.
bug: during the development period the product error may be 
occur this kind of error called bug.

bug, error,these r the issue which reduces the quality of
the softwarte

Defect is something is not working according to the
requirement OR Deviation from requirement specification.

Bug is the informal name given to the defect.

Error is generally used by the developers
i.e compile time error and run time error.

Failures are caused by the defects.