They are called electron clouds because, 1) they are made up of electrons and 2) when seen in certain microscopes and in theory they look like clouds. Now I'm going to explain 2 in more detail. The cloud part is derived from the fact that what we think of electron orbits being defined circular orbits is false. The motion of electrons in an atom is undefined and unclear, but remains in a certain area- the electron cloud. When you hear the term, electron orbital, that is just the area in which you should expect to find an electron about 90% of the time.
