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's

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

Error: A failure to complete a task

Defect: A fault or malfunction , error or irregularity.

Bug: this means is that if you don't know how to get around this, you may loose some of your work.

Error: The Difference Between Actual & expected Result.

Defect: Any error in the software that is detected after the application is released.

Bug: Any error in the software that  is detected before the application is released

Error: Any functionalty is wrong than its called Error.

Defect: If this incorrect functionality occour by tester then it is called Defect.

Bug: If this incorrect functionality Confirmed by developer then it is called Bug.