Subdomains are extensions of the main domain name which separates the site into various configurations. Subdomains act as folders that categorize the main website into detailed sections. Large websites that need to store a massive amount of information in different directories use subdomains. Most web hosting providers allow customers to create an unlimited number of subdomains.
Hey Carol.P,
Yes, you are right.
Subdomains are extensions of the main domain name which separates the site into various configurations.
Many organizations uses subdomain concept to assign a unique name to the separate service/department.
For Eg. "mail.domain.com" is subdomain for the domain "domain.com" for the mail service.