Measuring Output Transformer Primary Topic Of Electrical Study

My husband is studying to be an electrician, and he has to pour over his books each day after he gets home from work. He was recently telling me about his latest subject which was about the applications for measuring output transformer primary. He was explaining to me for example, about a 4k primary, as well as other degrees of primaries and how they function. It all really just seemed like trying to understand Chinese to me, but he understands it all quite well, since he has a rather brilliant mind, and can grasp these concepts much more easily than I can.