Definition of subdomain
Sub-domains are extensions of your domain name or you can consider subdomain as a second website, with its own unique content, but there is no new domain name. Instead, you use an existing domain name and change the www to another name.
For example if you register yourdomain.com and host this domain The subdomain name looks like blogs.yourdomain.com, sales.yourdomain.com.
In general subdomains are useful to split your large website to different small websites or if you want to distinguish and identify each site by using subdomains for each one.
In all of our hosting plans you can create unlimited sub domains