German, meaning "health". Used to wish someone "health" after sneezing. It has been exported, but seems primarily to be used in the US. Similar is "bless you"
A petty government official or politician involved in enforcing pandemic public health regulations. This is a 'Karen' or 'Chad' with the power of the State behind them.
The Gesundheitsfuhrer is confronting those without face diapers and writing them tickets in front of Walmart.
Used as a reply in certain contexts when someone has just said something quite verbose or confusing. "Bless you" can be used in the same way in this sense. Not all native speakers of English use it.
From the A Way With Words (waywordradio.org) radio show, Aug. 23, 2010:
I forgot to tell you, I sneezed at work the other day and farted at the same time. Ron said "gesundheit", so I'm fairly sure he heard the fart also. It was loud!