The "electron cloud" refers to the region around an atomic nucleus where electrons are likely to be found. Instead of moving in fixed orbits, electrons exist in a cloud-like distribution, which represents the probability of finding an electron in a particular area. This concept is a key part of the quantum mechanics framework that describes atomic structure. In the electron cloud model, the density of the cloud indicates where electrons are most likely to be located. The shape and size of the cloud vary depending on the type of atom and its energy levels, influencing the atom's chemical properties and interactions with other atoms.