The phrase "just-in-time" can be used for other things besides compilation (it's often used for manufacturing, for instance). I think it's a helpful way to describe lots of things, and that we shouldn't try to limit its usage in tech to just compilation.
JIT compiling is the term your most used to it being used with but JIT has been around in other fields for longer, and just means what it says... Just In time :)
And JIT just as in "just in time" configuration of Wire guard. Once the configuration has been done, their stack stays out of it.