(Magick is a spelling of magic, used by some, to differentiate "true" magic from illusion or stage magic) a way of influencing the world through supernatural, mystical or paranormal means.
Ritual or devised acts related to the use of magic, for worship of, or rehearsal of principles embodied in magic.
A spell is the basic mechanism of religious magical practices. It consists of a spoken or written formula which is used in conjunction with a particular set of magical ingredients. If a spell is properly executed and fails to work, then the spell is a fraud. However, in most instances, the failure of a spell to bring about the desired effect can be attributed to the failure of the person executing the spell to follow the magic formula to the letter.
Generally speaking, there are two types of magic: Contagious magic and sympathetic magic. Contagious magic involves the use of physical ingredients which were once in contact with the object or objects one hopes to influence with a spell, and sympathetic magic involves the use of physical objects which resemble the object or objects one hopes to influence.
"Theurgy" describes magic involving the action of God or some other personified supernatural power.