Theory of WavePorts and LumpedPorts

So far most questions here about waveports and lumpedports have all been about assigning them in various softwares. I couldn't find material explaining how waveports and lumpedports work. I am building an FEM solver(3D) as a part of my thesis and I was stuck at assigning ports basically the physics of it. Could someone please share some material they have read or explain about waveports and lumpedports? What does it mean to assign a waveport and lumpedport. If I were to take my tetrahedral mesh, how does assigning a waveport/lumpedport alter the nodal potentials etc.

Thanking You
Regards