What Is a Bug?

Terms for Software Failures

Depending on where you're employed as a software tester, you will use different terms to describe what happens when software fails. Here are a few:

Defect	Variance
Fault	Failure
Problem	Inconsistency
Error	Feature
Incident	Bug
Anomaly

(There's also a list of unmentionable terms, but they're most often used privately among programmers.)

You might be amazed that so many names could be used to describe a software failure. Why so many? It's all really based on the company's culture and the process the company uses to develop its software. If you look up these words in the dictionary, you'll find that they all have slightly different meanings. They also have inferred meanings by how they're used in day-to-day conversation.

For example, fault, failure, and defect tend to imply a condition that's really severe, maybe even dangerous. It doesn't sound right to call an incorrectly colored icon a fault. These words also tend to imply blame: "It's his fault that the software failed."

Anomaly, incident, and variance don't sound quite so negative and are often used to infer unintended operation rather than all-out failure. "The president stated that it was a software anomaly that caused the missile to go off course."

Problem, error, and bug are probably the most generic terms used.

For the purposes of this book and much of the software industry, a software bug occurs when one or more of the following five rules is true:

1. The software doesn't do something that the product specification says it should do.

2. The software does something that the product specification says it shouldn't do.

3. The software does something that the product specification doesn't mention.

4. The software doesn't do something that the product specification doesn't mention but should.

5. The software is difficult to understand, hard to use, slow, orin the software tester's eyeswill be viewed by the end user as just plain not right.