In the computer world, a bug is an error in a software program. It may cause a program to unexpectedly quit or behave in an unintended manner. For example, a small bug may cause a button within a program's interface not to respond when you click it. A more serious bug may cause the program to hang or crash due to an infinite calculation or memory leak.
From a developer perspective, bugs can be syntax or logic errors within the source code of a program. These errors can often be fixed using a development tool aptly named a debugger. However, if errors are not caught before the program is compiled into the final application, the bugs will be noticed by the user.
Because bugs can negatively affect the usability of a program, most programs typically go through a lot of testing before they are released to the public. For example, commercial software often goes through a beta phase, where multiple users thoroughly test all aspects of the program to make sure it functions correctly. Once the program is determined to be stable and free from errors, it is released the public.
Of course, as we all know, most programs are not completely error-free, even after they have been thoroughly tested. For this reason, software developers often release "point updates," (e.g. version 1.0.1), which include bug fixes for errors that were found after the software was released. Programs that are especially "buggy" may require multiple point updates (1.0.2, 1.0.3, etc.) to get rid of all the bugs.
Updated: December 17, 2008