Why there is a "d" after the name of processes like syslogd and httpd ? What is its significance ?
The d is short for daemon. A daemon is a long-running process that provides some sort of service.
httpd and syslogd are daemons, also known as background processes. They are typically not directly controlled by an end user, but rather run continually and provide a service or run a process which continually waits for a query or request.
httpd, for example, waits for clients to request its content, and syslogd is continually listening for logs to be sent to it so they can be stored. sshd is another well-known daemon which is continually listening for a remote client to request to establish a SSH connection to the device.