Difference between defect, error and failure?

Error : A discrepancy between a computed, observed, or measured value or condition and the true, specified, or theoretically correct value or condition. See: anomaly, bug, defect, exception, and fault

Failure: The inability of a system or component to perform its required functions within specified performance requirements. See: bug, crash, exception, fault.

Bug: A fault in a program which causes the program to perform in an unintended or unanticipated manner. See: anomaly, defect, error, exception, fault.

Fault: An incorrect step, process, or data definition in a computer program which causes the program to perform in an unintended or unanticipated manner. See: bug, defect, error, exception.

Defect: Mismatch between the requirements.

http://software-testing-faq.blogspot.in/2007/08/difference-between-defecterrorbugfailur.html

http://www.sqatester.com/bugsfixes/bugdefecterror.htm