Whenever I move, that's Aikido.
O Sensei, Morihei Ueshiba
Aikido is a Japanese martial art developed by Morihei Ueshiba (often referred to by his title 'O Sensei' or 'Great Teacher'). On a purely physical level it is an art involving some throws and joint locks that are derived from jiu-jitsu and some throws and other techniques derived from kenjutsu. Aikido focuses not on punching or kicking opponents, but rather on using their own energy to gain control of them or to throw them away from you. It is not a static art, but places great emphasis on motion and the dynamics of movement.
Upon closer examination, practitioners will find from Aikido what they are looking for, whether it is applicable self-defense technique, spiritual enlightenment, physical health or peace of mind. O Sensei emphasized the moral and spiritual aspects of this art, placing great weight on the development of harmony and peace. "The Way of Harmony of the Spirit" is one way that "Aikido" may be translated into English. This is still true of Aikido today, although different styles emphasis the more spiritual aspects to greater or lesser degrees. Although the idea of a martial discipline striving for peace and harmony may seem paradoxical, it is the most basic tenet of the art.
We could attempt to pigeonhole Aikido into a synopsis of X number of words, but that would not do it justice, so we leave the practitioner of Aikido to find out what Aikido is for themselves without any preconceived notions.