I think the wiki does contain a written down definition:

I am sorry, but that is not specified at all. If I give you a specific problem (I have a list of them right here!), will you be able to tell me what "the TDT answer" should be? The way people seem to use TDT is as a kind of "brand name" for a nebulous cloud of decision theoretic ideas. Until there is a paper and a definition, TDT is not a defensible point. It has to be formally written down in order to have a chance to be wrong (being wrong is how we make progress after all).

If it's a set of related decision theories, fine -- tell me what the set is! Example: "naive EDT" is "choose an action that maximizes utility with respect to the distribution p(outcome | action took place)." This is very clear, I know exactly what this is.