Not to be confused with the Martial Art Kempo, Kenpo is a Chinese form of Karate. Like most forms of Chinese Karate (and contrasting with Korean and Japanese, which are considered "linear"), Kenpo embraces circular movement and more than one simultaneous move. Because of this, Kenpo is sometimes called "non-linear". It is also somewhat less choppy (as in "not smooth," but the other definition holds too; chops are not quite as common in Kenpo) than other forms of Karate, such as Shotokan.
Kenpo also uses Chinese stylings such as non-conventional strikes (fanned-out eye gouges, strikes where the hand is shaped like a crane, palm strikes, etc.) and parries (Japanese and Korean styles more often use blocks, which meet a blow as opposed to redirecting it). Some other interesting things in the style include foot manuevers such as "step-dragging" (stepping with the front foot and dragging with the back almost simultaneously, making a sort of side-step shuffle).
There are two forms of Kenpo: Chinese Kenpo and American Kenpo. The latter has quite a following in America, being beaten out practically by just kickboxing and Tae Kwon Do.
See also: Chinese Kenpo, American Kenpo, Ed Parker