If an electron mass moves in varied motion forming an orbital cloud around atom why do they call it a wave?

Answer 1

there is one more reason called the De Broglie wave particle duality which states that wavelength = h/p
where h is heisenberg constant and p is momentum this states that all matter has wave associated with it higher the mass lesser the wave character. so electrons having low mass and high speeds have greater wave character. and as due to uncertainty principle we can pinpoint position associated with an electron we can represent it more easily with the wave associated with the electron.
hope this helps

Answer 2

Because you cant predict where the electron is, only the probability where it might be. Futhermore, electrons exist in superposition, until we observe them, so therefore they are a wave function. They are only particles when we look at them at a particular point in time. The real reality is they are neither a particle nor a wave and both at the same time, but this gets rather deep.