A daemon is a background, non-interactive program. It is detached from the keyboard and display of any interactive user. The word daemon for denoting a background program is from the Unix culture; it is not universal.
A service is a program which responds to requests from other programs over some inter-process communication mechanism (usually over a network). A service is what a server provides. For example, the NFS port mapping service is provided as a separate portmap service, which is implemented as the portmapd daemon.
A service doesn’t have to be a daemon, but usually is. A user application with a GUI could have a service built into it: for instance, a file-sharing application.
For more details: https://askubuntu.com/questions/192058/what-is-technical-difference-between-daemon-service-and-process