I'm a bit confused on some of the terminology involved in my assignment, which is shown in the following image:
I understand the main idea behind residual analysis is checking if the main assumptions are in line. This usually involves plotting residuals against fitted values and getting a normal probability plot for general diagnostics. The assignment is specifically asking to check if the two-way interaction terms (in relation to the residuals) are necessary for the model.
My main questions are: What exactly is a two-way interaction term? What characteristics of the residuals justify a two-way interaction term?