What is a daemon?

In UNIX, a Daemon stands for Disk and Execution Monitor. A daemon is a long-running background process that answers requests for services. The term originated with Unix, but most operating systems use daemons in some form or another. In Windows NT, 2000, and XP, for example, daemons are called “services”. In Unix, the names of daemons conventionally end in “d”. Some examples include inetd, httpd, nfsd, sshd, named, and lpd.