What is a domain?
Domain names are used in URLs to identify websites.
For example, in the URL
https://www.search.io/faq/getting-started the domain name is 'search.io'.
Search.io only counts domains towards your plan where the root domain is different, e.g., if we see the websites www.acme.com, acme.com and blog.acme.com as one domain but acme.com and acme-blogs.com are two different domains.