#GtkIconTheme provides a facility for looking up icons by name and size. The main reason for using a name rather than simply providing a filename is to allow different icons to be used depending on what “icon theme” is selected by the user. The operation of icon themes on Linux and Unix follows the Icon Theme Specification There is a fallback icon theme, named hicolor, where applications should install their icons, but additional icon themes can be installed as operating system vendors and users choose.