What are hostnames?

Hello. I want to purchase a private SSL certificate. I see the difference between “Dedicated SSL” and “Dedicated SSL with Custom Hostnames” is that with the latter, I get 50 hostnames/wildcards.

I don’t know what hostnames are. One way I’m interpreting this is if I get a regular Dedicated SSL, only my homepage will be protected and NOT any of the pages on my website. For example, only www.mydomain.com is covered but not www.mydomain.com/about

Am I understanding that correctly?

Thanks in advance.

A hostname is the name of a host, which means a server/machine in this context.
.https://en.wikipedia.org/wiki/Hostname

www.mydomain.com would be a hostname, mydomain.com would be a different one, and ftp.mydomain.com is yet another.

/about is part of the path and does not refer to the hostname. The two URLs you posted you point to the same hostname.