Will is a philosophical concept that is defined in several different ways. Most commonly as the ability to "choose" or make a decision.
Nietzsche defines will similarly to the "any internally motivated action" usage, but more narrowly. In this sense, will is more a "creative spark," a certain independence and stubbornness.
See free will for more on the non-theological aspects of free will. See Free will in theology for more on the debate on free will in general. This article discusses the doctrine of free will as it has been, and is, interpreted within the various branches of Christianity, Judaism, Islam and Hinduism.
A will is a legal declaration that disposes of a person's property when that person dies.