If Type is set to Heat Generation, then the dialog will look as shown below.
Heat generation can be applied to bodies, surfaces, and curves. When applied to curves, the elements along the curve take on the heat generation. When applied to surfaces, the elements on the surface will take on the heat generation.
Heat generation can be both time and temperature dependent. It is time dependent when transient heat transfer is selected, and it is temperature dependent when nonlinear heat transfer is selected.
Heat generation loads can have a variable load definition as well as custom display properties such as color, size, and density.