what is daemon

They are the processes which run in the background and are not interactive. They have no controlling terminal.

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.

Daemon stands for Disk and Execution Monitor. A daemon is a long-running background process that answers requests for services.

Many system functions are commonly performed by daemons, including the sendmail daemon, which handles mail, and the NNTP daemon, which handles USENET news.
Many other daemons may exist. Some of the most common daemons are:
  •  init: Takes over the basic running of the system when the kernel has finished the boot process.
  •  inetd: Responsible for starting network services that do not have their own stand-alone daemons. For example, inetd usually takes care of incoming rlogin, telnet, and ftp connections.
  • cron: Responsible for running repetitive tasks on a regular schedule.