When a sample of atoms is heated and releases light of certain wavelengths, it is called what?

The answer is emission spectrum. It is the range of frequencies of electromagnetic radiation produced because of an atom or molecule generating a transition from a high energy state to a lower energy state. The photon energy of the produced photon is equivalent to the energy change between the two states. There are many conceivable electron changes for each atom, and each change has a precise energy difference.