Bug Life Cycle - Quality Testing.flv
A fault in a program, which causes the program to perform in an unintended or unanticipated manner.
Lastly the general definition of bug is: "failure to conform to specifications".
If you want to detect and resolve the defect in early development stage, defect tracking and software development phases should start simultaneously.
We will discuss more on Writing effective bug report in another article. Let's concentrate here on bug/defect life cycle.