A bug happens when a tool does not do what it should do. For example, the famous Y2K bug had the potential of showing the wrong time. GIGO, which stands for Garbage In Garbage Out, is a different situation in which the tool performs what it should do but it is applied in a place that does not make sense.
Explanation:
When test engineer find any error in the application they called it as bug. Bug is informal name to Defect which is flaws or misatkes in the Code or Design. Error is any mistake done by the user while using the Apllication or Software. Failure due to any error or defect if the software will not work properly .
