The Elder Scrolls has a lot of sprites, from Altmer to Dunmer, with quite a few lineups. However, not all of them have a playable appearance. Take the Snow Elves of Skyrim, or even the Dwemer of Morrowind. We'll meet them, but we can't have the player character directly represent them. Usually, that's because they're extinct or endangered, but Maormer or sea elves are an exception.
They are abundant and come from a continent to the south, the Summerset Isle of Pyandonea. That's why they can't be played in any of the major Elder Scrolls games, they don't live in Tamriel. But they do invade frequently due to the ongoing feud with Altmer. Since the First and Second Ages, they have tried time and time again to conquer Summerset. Players need to constantly collect ESO Gold while learning about these Sea Elves, so as to go further in the game.
There is an ongoing competition between Maormer and Altmer. But the origins of this ancient discord are often up for debate. Some believe that Maormer was originally exiled from Summerset, evolving into the Sea Elves as the Altmer did from the Aldmer. But it is more likely that Maormer Buy ESO Gold, in the original elven homeland of Aldmeris.
Not much is known about the Maormers in the First and Second Era, other than their constant invasion of the shores of Summerset in an attempt to wrest them from the Ultramers. They fail every time. But during the Three Flags War (when The Elder Scrolls Online happened), Maormer did break into Tamriel by ruling over an island of Elsweyr called Kenarthi's Roost.
Maormer is an interesting group and plays as Altmer's main antagonist, much like Dwemer did for Chimer before Chimer became Morrowind's white-skinned Dunmer. Maybe one day we'll see this feud in a mainline game, maybe even The Elder Scrolls 6. But for now, they're still mysterious groups from far-flung lands we haven't seen yet. And for those players who want to buy ESO Gold, IGGM is a good choice.