Error-Bug-Defect
Error
Deviation from expectations.
Cannot be avoided
Need not affect normal behavior of system.
May be a problem or suggestion.
Eg. : runtime errors memory leakage etc
Bug
Unwanted and unintended properties of a program
Cause the program to malfunction
Error with impact on normal behavior of system
A concern about quality of product.
Defect
Bug causing failure of system.
A concern about reliability of product.
Eg. : Missing user requirements or functionality.
Just adding to my previous comments.
Pradeep R