Well, it is deployed regularly by people with a broad spectrum of "capabilities"...so what could it mean? Would the meaning (as it is used, and perceived) not also be a broad spectrum, that perhaps does not nicely intersect with a rigorous and comprehensive definition (that itself doesn't rely on numerous other complex compound terms, each of which suffers from the same problem, and others), which to my knowledge doesn't exist?
In simple terms, I just think it is just making effort to present the most robust and accurate case you can.
This involves questioning your work/thoughts before presenting/embracing them.
It involves being able put yourself in a skeptical position to it, and generate your own constructive feedback.
In some ways, it reminds me of the HN guidelines "Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith."
Take this for example:
https://en.m.wikipedia.org/wiki/Critical_thinking
Could it be something like a unicorn, or a God, or pornography?
https://en.m.wikipedia.org/wiki/I_know_it_when_I_see_it
Members of The Rationalist community are (self-)reputed practitioners of the craft...but then you can regularly read threads like this:
https://old.reddit.com/r/slatestarcodex/comments/1e2ow7e/so_...