Simple Wikipedia definition of Bug is: “A computer bug is an error, flaw, mistake, failure, or fault in a computer program that prevents it from working correctly or produces an incorrect result.
Bugs arise from mistakes and errors, made by people, in either a program’s source code or its design.”
Other definitions can be:An unwanted and unintended property of a program or piece of hardware, especially one that causes it to malfunction. or a fault in a program, which causes the program to perform in an unintended or unanticipated manner.
Lastly the general definition of bug is: “failure to conform to specifications“.