Atomic means relating to atoms, the incredibly tiny building blocks that make up everything around you: the air you breathe, the water you drink, your desk, your body, even this page. An atom is so small that millions could fit across the width of a single human hair.

Scientists talk about atomic structure when they study how atoms are built, with a dense nucleus at the center surrounded by electrons. Understanding atomic structure helped scientists unlock enormous amounts of energy: atomic energy or atomic power comes from splitting atoms apart or fusing them together, which releases tremendous energy. The first atomic bombs in the 1940s showed this power's devastating potential, leading to debates about nuclear weapons that continue today.

When something is described as atomic in everyday conversation, people usually mean it's extremely small or fundamental, like breaking a problem down to its atomic parts: the smallest pieces you can't divide further. In computing, an atomic operation is one that happens all at once, completely, without interruption.