The region around the atomic nucleus where the electron is mostly found is called the electron cloud or atomic orbital. This region represents the probability distribution of the electron's position, meaning it is where the electron is most likely to be located at any given time, rather than a fixed path or orbit

. The electron cloud is not a sharply defined boundary but rather a fuzzy region where the density of the cloud corresponds to the probability of finding an electron. It is densest near the nucleus and gradually decreases with distance, reflecting that electrons are more likely to be found closer to the nucleus but can be found at various distances depending on their energy level

. In quantum mechanics, these regions are described by atomic orbitals, which are mathematical functions that give the probability density for an electron's position. Different orbitals (s, p, d, f) have different shapes and sizes, and the electron cloud is essentially a visualization of these probability distributions

. In summary, the region around the nucleus where the electron is mostly found is the electron cloud , defined by the electron's probability distribution within atomic orbitals.