Somehow, I feel clear about definitions of daemon and server after learn a little bit about X11. So, I would like to have verification to my definitions as below.
Daemon is a process that is not associated with any terminal (has no controlling terminal).
Server is a process usually but not necessarily a daemon. Examples of daemon server are sshd and sftpd. Example of non-daemon server is X11. X11 has terminal associated with it, usually tty7.