One of the three off-shoot campaign settings to Forgotten Realms, alongside Kara-Tur and Al-Qadim. Like its counterparts, it focuses on an "ethnically different" area of the Toril world - in this specific case, a South America expy, in contrast to the Arabic Al-Qadim and the "Oriental" Kara-Tur.
Noted for being pretty well researched, for the time, but quite shamelessly ripped wholesale from the actual lore and history of South America, complete with the invasion of Conquistador-expies (a Helm-worshipping legion of mercenaries) who commit such brutal atrocities against the natives that Helm has to found a whole new Paladin order to try and make up for the shit they did.
After Tomb of Annihilation was released, Maztica became legal to post content for on the DM's Guild. A fan group has made a huge translation of the setting to Dungeons & Dragons 5th Edition... as to whether it manages to be something more than "South America ported wholesale to the Realms", well...