Organisms refer to complex UI components made up of groups of molecules and/or atoms and possibly other organisms. These are relatively complex sections of a user interface that form distinct parts of a system. For example, a header with a logo, navigation, and search form might collectively be referred to as an organism.

You can see that on an individual level, organisms don’t provide a whole lot of user value, but they’re key elements to an overall design. Without organisms, the final product would lack a lot of functionality.