When a software application is created, and major updates are made, the version number is often assigned to the software. Manufacturers also add a software build number to the version when smaller updates are made. The software build acts like a sub-version number. Patches for fixing bugs, issues (mostly small issues, but sometimes larger issues as well) and sometimes even minor feature additions often result in a change to the software build.
Keeping software up to date requires knowledge of the latest software build, as well as downloading and installing the patch that corresponds to it. Also, when needing technical support for a software application, the support staff often ask for the software build for your software, to better assist with issues or general help. Issue resolution may be dependent on the software build as some issues are specific to one software build, and the solution only works for that build and no other builds.