For the legal document dealing with disposal of property at death, see will (legal document). For the religious concept, see free will.
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.