If that means nothing to you, you're probably not very interested in The Elder Scrolls Online, which prominently features an event known as the Soulburst four years before the game takes place. So could this trademark be the name of an expansion? Upcoming content for another game in the franchise tying into this event? A prequel game to help excite players? On these matters (and many others) the trademark applications are entirely silent.
There's certainly some chance that this is just a coincidence and the trademark pertains to a completely unknown game, of course. You're welcome to speculate about that in the comments. Odds are good that it's a bit of a peek behind the veil... though a peek at what remains unclear.