From The Art and Popular Culture Encyclopedia
Supplication (also known as petitioning) is the most common form of prayer, wherein a person asks a supernatural deity to provide something, either for the person who is praying or for someone else on whose behalf a prayer of supplication is being made.
The concept is perfectly at home with secular use. The supplicant may also be described as a suppliant but the former word is more commonly used. The key meaning is of a request by the lesser person in an acknowledged unequal relationship.