Error: it is deviation from logic,syntax or execution.
there r 3 types of errors
syntactical error: it is deviation from syntax of program
logical error: it is deviation from logic of the program.
executional error: this occurs during executing the program.
Deffect: when the error is discovered by the tester then it 
is called deffect.
bug:if the developer accepts the deffect then it is called 
bug.