What is a trait called when it is controlled by more than one gene?
A polygenic trait.
A trait that is controlled by more than one gene is called polygenic which translates to "multiple genes". The genes work together to make one trait. Examples are skin, eye and hair color.
It is important not to confuse polygenic with multiple alles. In that case one gene has more than two alleles. An example of multiple alleles is blood type.