The short answer to "what is a suzerain?" is "overlord". The details are here in the definition.
The longer answer to the same question is "Suzerain is a universe created by Savage Mojo, and it is just like the real world but with magic, focusing on heroes who can travel to different parts of time and space. A magical past, present and future awaits them."
"The Suzerain universe is a complex mix of places and times. In fact, it’s every place and every time. In fact, it stretches outside of time as we know it. In fact, it stretches beyond the idea of ‘places’ as we know it.
Suzerain defines locations as realms, whether they’re mortal realms or immortal realms. Figuring out what realms exist can be tough, which is where the Celestial Map comes in. You can see the map on the Welcome page of this website. It’s the main image on the page, full of intriguing links to click on". -from the Savage Mojo website
Check out the Celestial Map. It's really cool.
Some of the realms in the universe have already been created (for example, Untamed Empires, which you may recall as the home of Mr. Vermilion's Carnival, among other things) but some realms have yet to be dreamed up.
Mechadia, the dream-vision of the Duke of Crossed Gears, is a combination of faerie lands and steampunk technology, and the Mechadia realm book is what Houser and I are writing right now. Well, not right now, because right now I am writing this blog post. But you get the idea.
Right now we're sketching out the world - where you can go, who lives there, what the conflicts are for characters to be involved in and beset by. I can't say too much, because that would spoil the book, but there WILL be Airship Pirates!