By itself, the term "relativism" is entirely vacuous: It doesn't mean anything. (Or it means everything, which is semantically the same.)
In a trivial, banal, vacuous and almost entirely uninteresting way, everything is "relative".
Even the truth of an ordinary statement of reality is relative to how the world actually is. Even the most hidebound Divine Command Theorist would admit, in this same trivial sense, that the truth of a particular statement about good or evil is relative to God's commands.
Most (if not all) of the work of our language and thought consists of determining and communicating relationships. The concept that everything is "relative" in this trivial, vacuous sense should not come a complete surprise.
In a related sense, every relation can be turned into an absolute by specifying all the parts of the relation. The example I gave in the earlier essay from physics was the transformation of relative velocity to absolute velocity-relative-to-coordinate-system-X.
We cannot talk about "relativism" or "absolutism" in a vacuum. If we're going to talk about relativism, we need to talk specifically about what's related to what. If we're going to talk about absolutism, we need to talk specifically about what's not related to what, or specifically about what relationships do need, to the exclusion of others, to be described to construct an absolute. This requirement holds whether we're discussing physics, ethics, aesthetics or directions to the grocery store.
Authoritarian writers and ethical philosophers have been very successful in using this vacuity as a framing and caging device. It's a classic switcheroo distraction technique used by bullshitters everywhere (and, sadly, no small few philosophers even in the canon):
- Find a word or phrase that's extremely broad
- Find some sense in which the phrase is patently ridiculous
- Explicitly define the phrase entirely in terms of the ridiculous sense
- (The first half of the switcheroo) Define your opponent's position in the broad sense of the phrase
- (The second half of the switcheroo) Argue that your opponent's position entails the narrow, ridiculous sense of the phrase
Here we can see a fairly blatant example of this technique. Happily, Cassandra is a very poor bullshit artist; she doesn't even try to hide the switcheroo. In this case, she switcheroos the meta-ethical subjective relativism of my position to the ridiculous notion of ontological subjective relativism. Other, more able bullshit artists usually relate "relativism" to the internally contradictory sense of metaphysical relativism and do a better job of hiding the switcheroo.
In ethics, the argument is not over whether ethics are relative, because everything is relative in the trivial sense noted above. The argument is really about what relation ethical statements discuss; i.e. about what relationship must be specified for a statement to have an absolute (singular and determinant) truth-value.
Another good example is how authoritarians switcheroo epistemic/ontological cultural relativism for meta-ethical cultural relativism. The ethical statement, "People in Islamic cultures approve of limiting the civil rights of women," is an unproblematic statement of the relationship between Islamic people and opinions about the civil rights of women, with an absolute truth-value under weak meta-ethical subjective relativism, and actually true.
Under authoritarian framing, though, the statement becomes the ridiculous epistemic/ontological relativistic version, "Because people in Islamic cultures approve of limiting the civil rights of women, it is therefore the case that it is good to limit the civil rights of women." The inference here is fallacious not because the antecedent is false (it's actually true) but because the epistemic/ontological material implication is either false or not truth-apt.
We should resist this framing for two reasons. The first is that it's fundamentally bullshit and we should resist bullshit on general principles. More importantly, if anyone is going to stake a strong claim to "absolutism" (in the bullshit sense of being relative only to mind-independent objective reality), authoritarians philosophy has the best case. Ceding the authoritarian bullshit definition of "relativism" actually hands them, if not the whole game, then at least an enormous advantage.
 If you're going to quote me, please quote the entire sentence including all the modifiers.
 I'm currently reading the magnificent book, Bullshit and Philosophy. Expect to see the word "bullshit" crop up often in my writing for a while.
 The statement "everything is relative" is an absolute; the statement is something, therefore, "everything is relative" is self-contradictory.
 Weak meta-ethical subjective relativism is just the strong definition of meta-ethical subjective relativism where "if" replaces "if and only if".
 i.e. we are drawing an ontological conclusion (limiting women's rights is good) from an epistemic basis (Islamic people approve of limiting women's rights).