A software bug is an error, flaw or fault in the design, development, or operation of computer software that causes it to produce an incorrect or unexpected result, or to behave in unintended ways. The process of finding and correcting bugs is termed "debugging" and often uses formal techniques or tools to pinpoint bugs. 

Bugs in software can arise from mistakes and errors made in interpreting and extracting users' requirements, planning a program's design, writing its source code, and from interaction with humans, hardware and programs, such as operating systems or libraries. Bugs can trigger errors that may have ripple effects. The effects of bugs may be subtle, such as unintended text formatting, through to more obvious effects such as causing a web application or website to crash, or even freezing a webpage/website. Other bugs qualify as security bugs and might, for example, enable a malicious user to bypass access controls in order to obtain unauthorized privileges.

A software application issue can be classed as a bug where:

  • The application crashes to code (excluding bugs resulting from third party products, e.g. "blue screen of death" or crashing in a third party data grid that we cannot control); or
  • The application displays data inconsistent with the specified business rules; or
  • The application is missing functionality specified in the specification; or
  • The page design/layout is substantially inconsistent with predefined requirements by the client as part of the design/layout agreement and documentation
Examples of what is not a bug:

  • Not being enrolled in course
  • Not being able to access a SharePoint website
  • Any problem caused by software or an application not written by the organization supplying the software
  • The customer requirement is/was not included in the user interface/specifications
  • The client decides that they don't like the look of the current form and wants the buttons at the bottom of the form instead of at the top, even though the form is substantially the same as shown in the specification
  • The original specification states that the total price excludes GST, but it really should have included GST; this is a change to the specification