CONCACAF is the continental confederation for North/Central America and the Caribbean nations. South America has its own confederation (CONMEBOL), as do the other continents (UEFA, AFCON, AFC, etc). There are a few weird standouts - Israel is in Europe for obvious geopolitical reasons, Australia left Oceania for better competition in the Asian confederation, and Guyana, Suriname, and French Guiana play in CONCACAF rather than in CONMEBOL even though they're physically in South America, because the CONMEBOL teams like their little club (I don't actually know the reasoning for that). Most confederations have at least one continental tournament played periodically, usually in the summer which is the typical time for international tournaments in the FIFA calendar. Some of these are fairly prestigious - most notably the Euros and Copa America (CONMEBOL).
The Caribbean countries outnumber the other nations in CONCACAF and thus control much of the governance.
One of the consequences of this is that the Gold Cup is played every other year rather than every four years like most continental tournaments, as a money grab. The stronger nations often send weaker rosters to some (or, going forward, possibly every) editions of the Gold Cup so their better players, who are often playing grueling seasons in Europe, can get an actual offseason and some fringe guys or future prospects can get some time. There's also ANOTHER continental competition (remember, money grabs) called the CONCACAF Nations league played every two years which USA/Mex/Canada seem to be prioritizing for their stronger teams because it's more spread out and less of a time commitment in a given summer. The US won the latest edition a few weeks ago.
Sometimes confederations invite guests to participate in their tournaments - Qatar bought their way into the last couple Gold Cups with "sponsorships". This often happens with Copa America because 10 teams is an awkward number for a tournament. The US is invited to (and hosting) the 2024 Copa America (again, money grab - if you want to make a bunch of money on an event, host it in America). Presumably they will field a strong roster for that tournament next summer.
More than you ever wanted to know. So I'll throw in one more note - if you watch US games against the various CONCACAF teams, it's important to leave your expectations at the door and embrace the CONCACAF suck. This goes triple with weaker rosters like we have for this tournament. Expecting the US team to look good against these teams is preparing yourself for endless frustration. The officiating will be beyond questionable. If the game's not in a major country, there's a good chance the field will look like a goat pasture. There will either be 4 people in the stands or the stadium will be threatening to collapse, depending on location. Gotta embrace it or just don't watch.
