The electron cloud model is a theory of the atom that comports with the modern understanding of quantum mechanics. The model dispenses with the classical "orbiting electrons" depiction and envisions electrons as holding indeterminate positions in a diffuse cloud around the nucleus of the atom.
Classical atomic physics described the atom as consisting of a nucleus, which consisted of protons and neutrons, surrounded by electrons, which were pictured as discrete particles with set orbits almost like the orbits of planets in a solar system. This model was falsified by the predictions of quantum theory, which offers an alternate vision of electrons as surrounding the nucleus in a diffuse cloud of probable positions.
The uncertainty principle prevents simultaneous knowledge of an electron's position and energy level. For each permissible energy level, the electron has a range of positions in which it could exist, and for every position it could be in, a range of energy levels is possible.
Factored together, these potential states form a cloud around the atom. The cloud is in some ways a mathematical abstraction, but the abstraction has a physical reality, as the electron clouds of neighboring atoms do not normally overlap, though the potential states of electrons in a single atom form a single, uniform cloud.