I feel that bug and defect are all the same. Some 
organizations use any discrepancy between actual and 
expected as bug and some as defect. The terminology we use 
is....a discrepancy is called error at the tester's site, 
it is called defect finally after accepted by the developer 
and as a bug when found in the software after release into 
production. Correct me if I am wrong.

"bug" is just a general and informal word for any error or 
defect. But we have to talk about some other terms -
 "error" and "fault" if we want to know "defect"...
"error" is formal term in software development/testing 
which refers to the fault discovered in the same phase 
where it is introduced. "defect" is formal term in software 
development/testing which refers to the fault discovered 
after the phase where it is introduced. "fault" consists 
of "error" and "defect".

in the testers point of view it is a bug

in the custmer point of view it is a defect

Tester will use the terminology "Defect" whereas Developer 
will use the term "Bug".

When ever we find a mismatch in coding then it is called as 
an error,and that error found out by tester in the testing 
stage is called as a defect,when that defect isaccepted by 
developers and client is called as an Bug

a bug is that if  the code has  bug the code could be 
processed it proceed with the next step but produce 
unexpected output
in the case of error the code cannot be processed it will 
not proceed to next step if error is present at that 
particular point it stops the functionality

The discrepancy between the actual and the expected result 
is said to be a bug.

Bug is the term that is used by the Test Engineer and 
defect is the term that is used by the developers.