Here's Stephen Jay Gould on what I mean:
It is a fact--in the exact sense I posted earlier--that we know biological evolution exists and all researchers accept it, the underlying mechanism are theorized, and we do not have all the answers. As he says, even a fact in itself is not absolute certainty, and a theory is an imperfect fact:
Moreover, "fact" does not mean "absolute certainty." The final proofs of logic and mathematics flow deductively from stated premises and achieve certainty only because they are not about the empirical world. Evolutionists make no claim for perpetual truth, though creationists often do (and then attack us for a style of argument that they themselves favor). In science, "fact" can only mean "confirmed to such a degree that it would be perverse to withhold provisional assent." I suppose that apples might start to rise tomorrow, but the possibility does not merit equal time in physics classrooms.
Evolutionists have been clear about this distinction between fact and theory from the very beginning, if only because we have always acknowledged how far we are from completely understanding the mechanisms (theory) by which evolution (fact) occurred.
Underlined by me for emphasis.