Aikido derives from Japanese forms of Martial Arts. It has roots in several other Japanese styles, such as Jujitsu and Judo. Aikido specifically refers to the style of Martial Arts that can be traced back to Morihei Ueshiba, known to Aikido students as O Sensei.
An accomplished martial artist, fencer and athlete, Ueshiba studied many stylse and arts. As his story goes, while he excelled in the physical aspects of all he did, he felt something missing. It wasn't until he turned to religion, including Shintoism, that he began to see martial arts as not only a physical training but a way to be one with the universe.
Ueshiba originally referred to his martial arts as "Aiki Budo". It isn't clear exactly when he began to use the term "Aikido"; but 1942 it was the name of the art Ueshiba taught and recognized by the Greater Japan Martial Virtue Society during the centralization of Japanese Martial Arts.
It was first introduced to the Western world by Minoru Mochizuki when he visited France to introduce the techniques to judo students.
Roughly translated, Aikido means in Japanese "the Way of Harmony and Spirit". While the founder did find his focus in religion, the student doesn't necessarily learn religion on the floor. Characteristic to Aikido, a practioner uses whole body unity in their movements in order to dislodge but not injure their opponents. Akikido is very strongly based on self-defense techniques. The movements are subtle, graceful and effective. As with many of the older budo styles of Japanese Martial Arts, it focuses on developing both the internal and physical aspects of its students.
Aikido has also gone by the name Aikibudo and Aikinomichi. Today, there are several different schools of teaching for Aikido throughout the world. The most well known ones are: Aiki-budo, Yoseikan, Yoshinkan, Aikikai, Iwama-Ryu, Shin-shin Toitsu Aikido.
For more information on Shintoism, please refer to the articles in our Japanese Culture site.