Since it was initially revealed last year at E3 2015, we still don't know a whole lot about For Honor. The same could be said for this teaser, but unlike a lot of the leaks and announcements that have fallen this week, For Honor has been successful at staying quiet.
The teaser trailer is a small cinematic showcasing a few glimpses of what is likely a Viking longboat heading towards a shore before a row of submerged spikes come up through the water to stop the invaders' advance.
For Honor's primary focus is something the developers are calling the "art of battle." As you fight, you can "feel the weight of the weapon in your hand, crash as you block the attack, and impact as you strike the blow." You will be able to play as Vikings, Samurai, and Knights while waging war in an online arena.
Source: [YouTube]