icontheme

An icon theme, or icontheme, is a curated collection of icons used by a desktop environment or application to visually represent actions, files, and apps. Icon themes allow users to customize appearance and maintain visual consistency across software by mapping standardized icon names to specific image assets.

Icon themes are governed by the freedesktop.org Icon Theme Specification, which prescribes a directory-based structure, naming conventions, and metadata. Themes typically live under /usr/share/icons or ~/.icons and may declare inheritance from other themes so missing icons can be filled by a fallback chain.

Icons are provided in bitmap formats such as PNG and vector formats such as SVG. Themes organize icons into sized folders like 16x16, 32x32, 48x48, and scalable categories for SVGs. An index.theme file in the root of the theme describes the theme's name, comment, and Inherits relationship and can also specify directories for different sizes.

Desktop environments look up icons by standardized names (for example, "document-open" or "preferences-system"). If a matching icon is not found in the current theme, the environment may fall back to a base theme such as hicolor, or to icons embedded with the application.

Icon themes are created and distributed by developers and communities. They commonly include numerous icons sized for various screen densities and adhere to a consistent visual language. Popular themes include Adwaita, Papirus, and Numix, and many themes are licensed under permissive licenses suitable for redistribution.

See also: iconography, user interface design, freedesktop.org Icon Theme Specification.