In this paper, we aim at a transdisciplinary approach to atomicity. We especially focus on the mathematical perspective and we highlight the intimate, usual, defining property of the atom of being, in a sense, the essential indestructible, indivisible, irreducible, minimal, and self-similar unity. Using notions, concepts and results, we try to answer the question "What is the atom?" from a mathematical perspective, offering at the same time a series of possible interpretations and meanings that exceed its strict limits.