It means the common essence of what it means to be human, totally separate from culture, race, era, gender, etc. I'd probably limit it strictly to the knowledge of one's own selfhood and mortality if I had to pick something: nothing else. Because I really don't believe in essentialism (that things/people have some kind of inviolable 'essence' separate from culture, morality, consensus, religion, etc) - at least not in any kind of significant way.
But... a lot of people do. So, when people use the phrase 'human condition', they usually use it as a vehicle for whatever they personally class as something innate to all humans, merely by virtue of being human - but saying that their opinion on that is objective and not open to change, difference or subjective disagreement. So, mostly I think it's fluffy, overwritten, horribly generalised bullshit
