What in the HELL does white supremacy mean?

I've heard that phrase used in SOOOOOOOOOOOOOOOOOO many contexts it makes my head spin.

Just as an example, the Rittenhouse case.  Everyone keeps talking about white supremacy this and white supremacy that - - if it means what I think it means, why are they using that term over and over??  There wasn't a black person in sight on ANY of the videos I watched of the Rittenhouse event.  Not. One. Black. Person.

But the factbombers over at MSNBC and CNN, etc., have nothing else to bitch about right now, so they're focused on this white supremacy gig.  It's just appalling.  I truly hope Joy Reid burns in hell for what she's said and for what she's implied over the past year and 3 months.  The woman is unbalanced, clearly.

So please, someone explain white supremacy TO BLACK PEOPLE, OK?  And then explain it to me.