Aikido is a martial art founded by Morihei Ueshiba (the man on the right). He is often called Osensei meaning "Great Teacher". Aikido is based on the principles of resolving conflict by non dissension. I have no intention of trying to describe what Aikido is because ... A. I haven't been doing it that long so I dont feel that I am qualified to do so.
B. It's very hard to describe!
What I will say about it is that I would recomend anyone at least trying it. On the physical level it based on turning your opponents force back on him/herself by means of throws, wrist locks, correct distancing and circular movements.