From Ubuntu man page for daemon
A daemon is a service process that runs in the background and supervises the system or provides functionality to other processes.
OK, so where did the name daemon come from.
From Wikipedia Daemon (computing)
The term was coined by the programmers at MIT’s Project MAC. They took the name from Maxwell’s demon, an imaginary being from a thought experiment that constantly works in the background, sorting molecules.
I know what you are thinking - thanks, but that really is of no help.
Take a few minutes to watch this YouTube excerpt from “The Story Of Information” With Professor Jim Al-Khalili (full)
So now when you hear the word daemon or see a Linux process that end with d such as httpd you will now have a better idea instead of, I will just go along with the name not really knowing why.