Subdomain

A subdomain is anything to the left of the domain you registered. If you own example.com, then blog.example.com, shop.example.com and anything.example.com are yours to create, for free, just by adding records in DNS. The www in www.example.com is a subdomain too, just a very common one.

They matter to investors mostly as a reminder of what you're not buying. Owning a subdomain on somebody else's domain, the way a free site builder gives you yourname.platform.com, means you own nothing. The platform does. That's the pitch for buying a real domain in the first place.

Search engines mostly treat a subdomain as part of the parent domain, though not entirely, and a subdomain with a bad history can drag on the main site.