Floquet Ports? When would you use them?

For those of use who need some things said in simple words before we start doing the difficult math..

It would be great if someone familiar with them could provide a succinct qualitative description of what is a Floquet Port, a Floquet Mode, and what would motivate trying to apply them.

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Where we have been so far..
Google "Floquet" and you discover it is "a branch of ordinary differential equation theory"
https://en.wikipedia.org/wiki/Floquet_theory
OK, such equations are encountered in wave theory..

More searching, and we discover there are expressions for "Simple Plane Wave (Fundamental Floquet Mode" - So there are "Floquet modes" presumably special compared to ordinary "modes"

Still not clear about Floquet Modes, we see there are also "Higher Order Floquet Modes" with complex exponential expressions. I kind of expected that.

We find "Floquet Ports" - as opposed to "modes, as a tool available in some simulators. Not sure now..
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PS Edit:
After more searching, I find they are often associated with simulating a cell that would be part of a larger array, to break up a huge and possibly un-viable calculation. Also, they seem to involve plane wave excitations of a specially useful solveable kind. Hmm.. I still don't understand them..