Aikido consists of a number of different styles that have been categorized as Old Schools and Modern Schools. The Old Schools were established as pre-war teachings that are considered to be pure and unrefined while Modern Schools are new variations of ancient teachings of Aikido that are taught today. The different styles of Aikido have been mastered by students of the Founder.
Aiki-Budo is an old school martial art that was introduced by Sokaku Takeda to the founder of Aikido, Morihei Ueshiba who further developed and mastered the style. Te word Budo is usually translated to "martial art." Aiki-Budo is the second variation of Aikido and the former is Aiki-jutsu.
Yoseikan Budo was founded by Minoru Mochizuki at the Yoseikan Dojo in Japan who was one of the students of Morihei Ueshiba. Yoseikan combines Aiki-Budo with elements of Karate, Judo, Kendo and other martial arts. The techniques of this style are focused on fundamentals including escaping from a grab. The attacks of Yoseikan Budo are meant to be effective and sincere.
Yoshinkan is a style of Aikido that was initially taught by Gozo Shioda, who was a direct student of Ueshiba, before the war. This style is considered a "hard" style because there is an emphasis on correct form rather than correct flow. When Shioda established the Yoshinkan style, he focused on maintaining a structured teaching centered on foundational techniques. This style continues to be taught to Japanese police officers.
While these are the three major pre-war teachings of Aikido, there are many offshoots in the Modern Schools. Founders of various styles have evolved from the original teachings of O'Sensei Morihei Ueshiba.