As spotted by bogorad222 and shared by various other sources, 'Starborn' has been trademarked by the Microsoft-owned company; relating to "downloadable computer game software via a global network". That sounds a lot like DLC to us.
The above Twitter account has also provided a little more context behind the name Starborn. As covered by the game's wiki, the name relates to Starfield "humans who have passed through The Unity, which allows them to travel between universes" in the team's sci-fi title.
Now, all of this isn't confirmation of any particular plan or type of DLC pack, in fact, it might turn out to be nothing at all given that trademarks are often filed and never used by video game companies. We do know that Shattered Space is coming this year though, and with Bethesda's Todd Howard confirming that more expansions are planned beyond that, Starborn could easily turn out to be the game's following DLC pack.
We'll keep an eye on this one and see where it ends up - and in the meantime, we can all look forward to the game's Shattered Space expansion later this year.