To Bottom Out

I use the verb phrase “bottom out” in a way that is incompatible with anything that Google knows of. I know no other phrase so I define it here until I learn better terminology.

When you explain a phenomenon A in terms of phenomenon B, we say that B is a lower level phenomenon. The lowest level is at the bottom and we say that bottoming out is when we get to the phenomenon that we feel that we need not explain.

Sometimes it refers the lowest level abstractions in some complex software design.