Atoms are the basic building blocks of matter. Applied to web interfaces, atoms are our HTML tags, such as a form label, an input or a button.

Atoms can also include more abstract elements like color palettes, fonts and even more invisible aspects of an interface like animations.

Like atoms in nature they’re fairly abstract and often not terribly useful on their own. However, they’re good as a reference in the context of a pattern library as you can see all your global styles laid out at a glance.