This is maybe the most obscure pull I’ve ever seen from a Star Wars thing. Taungsday–mentioned in a jokey “Mondays, am I right?” kind of way in this episode–is the third day of a Coruscant week, and this was established in a now-deleted blog for Hyperspace subscribers in 2009. And no Star Wars character had ever mentioned it in-universe before this episode of The Mandalorian. There’s a lot more meaning to this name, though, than just its weird origin.
The Taung, who are an alien species native to Coruscant, have no presence to speak of in the current Disney canon outside of this one bit, but they were important to the galaxy’s history in the old Expanded Universe canon. Back then, the Taung lived on Coruscant before it was a planet-wide city, but they were largely supplanted by humans in ancient times before the Galactic Republic was formed with the planet as its capital.
When those ancient humans drove most of the Taung off Coruscant, they fled to the outer rim, where they stayed for centuries until a warlord united the entire species for a war of conquest against a new planet that would become their new birthright as a species. That planet was Mandalore, and these Taung were the original Mandalorians.
None of that is part of the current Star Wars continuity, but we’re talking about hundreds of thousands of years before the time of any Star Wars story. This doesn’t have much bearing on the present so you could include this in your headcanon without it affecting anything else, really.