HTTPD stands for Hypertext Transfer Protocol daemon (i.e., Web server). It is a software that runs in the background and waits for incoming requests,
The httpd.conf file defines configuration settings for the HTTP protocol and for the operation of the server. It is only accessible by a system administrator unless you have a Dedicated Server or VPS.
If you have Dedicated Server or VPS, cPanel installs the configuration file in /usr/local/apache/conf/httpd.conf and then creates a symlink to /etc/httpd/conf/httpd.conf so both paths will work on a cPanel installation.