I think there are several slightly different variations, but generally a trampoline is something like this pseudo-code:

    while (next_fn_to_call != nullptr) {
       next_fn_to_call = next_fn_to_call()
    }

So each function potentially wants to call a new function once it's done, but you don't want to blow the stack (or maybe use a stack at all) so it returns that function (pointer) rather than calling it. Then you need a little loop to call the return value: that's your trampoline.

The article is potentially a bit lower level given it's talking about things down at the CPU level, but I imagine its a vaguely connected idea.