all are different

Bug : Discrepancy in the application functionality
Error : Mistakes in coding
Defect : Deviations from the requirements

ERROR:IF it is found in developers Environment by 
developers only.
BUG:Testers find while testing an Application/build.
DEFECT:If the developers accept the bug and fix it than it 
defect.

A mistake in coding is called error. This eror is found by 
tester during testing called defect or issue.This defect or 
issue accepted by developers to reslove called bug.

Error : It is the Deviation from actual and the expected value.

Bug : It is found in the development environment before the
product is shipped to the respective customer.

Defect : It is found in the product itself after it is
shipped to the respective customer.

As per laxmi everything is right except about "Defect"

If anything is not working propely as per the requirement 
at client site that time customer says it is a defect..

As per me
Error - Developer 
Bug - Tester
Defect - Customer

Hi 
As kashinath and lakshmi told its absolutely correct
error leads to bug and bug leads to defect

Mistake in code is called error due to error test engineer 
getting mismatch in application is called defect. Defects 
are accepted by the developers is called bug.

Bug: this is a manifestigational error, in the sence we can 
visible frequently when ever the program running 
continuously..that is why Y2k call as bug not as defect.

Defect : this is deveation/difference of our test cases 
with respective requirements and due this test cases will 
not be meeting the requiremts as well. Those erros has 
called Defects.

error: this is general error, normally programer will be 
getting it may be syntax errors or run time errors

Error:  A mistake in a coding is called Bug

Defect : Due to errors in coding testing engineers are 
getting mismatches in the application build these are 
called defects or issues

Bug :these defects or issues are accepted by developers to 
be solve then it is called bug.

Error:These are generally coding mistakes done by the
developers.

Bugs:Whenever an issue in not in compliance with the
functional requirement specification(FRS) its a bug in the
software.

Defects:Whenever the issues are not in accordance with the
customer requirement specification (CRS) then its a defect.