Demons. Few things capture the imagination of a magician as much as the idea of spiritual beings who will carry out the magician’s every whim or desire.
Many cultures throughout the millennia have had similar concepts of “lesser” deities who could be persuaded to help man with his life and his problems. The word “genie,” for example, comes from the Latin genius, which is a guardian or “tutelary” spirit.
Arabic and Islamic mythology have the concept of the djinn. The djinn are spiritual beings, lesser than angels, that can help or hinder man depending on their own nature as good or evil.
The root of the word demon itself comes from daemon (or dæmon) which is the Latinized form of the Greek δαίμων (“daimôn”). Daimons in Greek were lesser divinities, or the souls of dead heroes. Originally, the Ancient Greeks had no concept of “evil” daemons, but as Christianity took hold, the concept of daemon slowly acquired the menacing and evil associations that the word “demon” has now. This sort of demon has become popular in movies beginning with The Exorcist in 1973. Needless to say, this sort of demon has nothing to do with the sorts of practical and useful daemons we use in magick. Therefore, I use the spelling daemon to refer to any spirit less than an angel, such as Goetic demons.
What is a “lesser” spirit?
A lesser spirit is anything lesser, or lower, than an angelic force. They are generally used for practical concerns.
In magick, there is a divide between the “angelic” forces and “daemonic” forces, which is essentially a measure of how close they are to the material plane.
Angelic forces are those closely related to God. They are spiritualized and tend to naturally inspire us and lift us closer to Godhead. Daemons are “lower”, “lesser”, or “blacker” because they exist closer to the material plane, hence their great power over it. However, being so close to earth and man, the heaviest of the planes, daemons are also more stubborn and likely to lead us astray than the angelic forces, hence their reputation as potentially negative or “evil.”
So why not just use angelic forces?
In medieval magick, things were extremely hierarchical. First, you invoked God and angelic names, and then you used their power to command the daemons. It was not considered an evil act to work with daemons as they were to submit to your Will, and your Will is considered to be an extension of divinity.
To ask an angelic force to do something as mundane as pay off your mortgage or get you a mistress would have been considered insulting to the angel. Instead, the dirty work of solving day-to-day needs and problems is left to the daemons.
 From the Arabic جني (jinnī).