The atom as a concept dates back to around 460 B.C. when the ancient Greek philosopher Democritus originated both the idea and the name. Though the idea was largely ignored by subsequent philosophers of his era, the concept eventually resurfaced and is now an indispensable component of modern physics.
Democritus postulated that in the process of breaking an element down there must be a final point where it cannot be broken further. This final, unbreakable piece, he named the atom. Though modern physics asserts that atoms can actually be broken into smaller particles, the atom remains the smallest complete individual unit of an element.