In short, they are your soul. The spelling is taken from the His Dark Materials books. The concept in the books was taken from Aristotle's concept of a daimon who was his spiritual guide.

A daemon in our world is incorporeal, more of a voice in your head. When people visualize them, they are usually animals. They can shapeshift to almost anything. Eventually they will settle as an animal that reflects your personality and character the best.
My daemon is settled as a red fox.
by Anacetios June 28, 2007
1.A type of demon in strict reference to a Greek definition rather than the often associated Christian interpretation. "Daemon" is actually the mis-romanization of the Greek word "Daimon" for there is no Greek dipthong for "ae". It is often used incorrectly by people attempting to sound pretentious, arrogant and self important who really no nothing of the subject they speak about.
"Through his spelling of 'daemon' it was clear that he was attempting to make himself sound intelligent, thus failing miserably."

"My Latin teacher kicks so much ass because we bitched together about pretentious assholes and their hilarious misusage of spellings and Greek adaptions such as 'daemon'."
by blubbernugget February 9, 2007
If you have a Daemon in your life you are extremely lucky. Daemon is usually a males name. He is kind and caring but it takes him a while to open up to you. once he starts opening up to you, you know he trusts you. He's impatient and determined. Once he gets his mind set on something you will have a hard time changing it. He does stupid stuff but he tries not to. Daemon is usually one to get all the ladies but when he is taken he stays loyal. He tends to hide his pain but when he shows it, its almost to late. He can scare you with some of his actions but he doesn't mean to. He tends to pouts if you don't give him attention.

pretty much someone you can trust your life with.
"Omg Daemon, you're amazing"
by ajlololol April 12, 2019
Unlike Demons, which are extradimensional creatures, Daemons are what are best described as negative beings, or walking vortexes of dark matter. They are beings of pure evil that are from a prallel universe. As soon as a gap is breached between our universe and theirs, a massive extinction often occurs. Daemons are unstoppable, except by the Demons and Gods.
The last Daemon invasion took place 65 million years ago, and wiped out the first truly intelligent civilization on earth.
by detranova December 3, 2003
Daemon is a name for a sweet, caring guy that will do a n y t h i n g to win a girl over. No matter where you end up, if you move or transfer schools, he will somehow always stick around for you. Even if it means staying up all night just to hear your voice. Has a super dirty mind, and is always making nasty jokes... but that’s who he is, and it’s kinda grown on you at this point. He’s socially awkward, and conversations with him are never boring. Don’t ever let him slip through your fingers 👌

Is also really easy to ship him with one of his gay guy friends 😝
Sarah: “Stop being weird! Yah nasty!”
Bee: “I don’t even want to know..?” *walks the other way while flinging her arms*
Gay Friend: “EAT MEEE DADDY! #ZAEMON WILL NEVER DIEE!”
Bee: “He’s being such a Daemon right now.. or whatever 😉”
by GeeSmiley September 23, 2018
Girl 1: Hey, did you just see that Daemon!?
Girl 2: Yeah! It looked pretty juicy!
by KHReborn February 13, 2012
A unix program that runs in the background of the system. Often signified with the -d suffix on the end of a program name.
mysqld
named
httpd
by Parallax July 3, 2003