Second Level Domain
The Second Level Domain, or SLD, is the data directly before the top-level domain (TLD).[1] For example, in www.domainname.com, “domainname” represents the second level domain, as the suffix "(dot)-com" represents the TLD. The SLD is generally the portion of the URL that identifies the website's domain name.[2] Usually, the SLD is determined and defined upon registration of a domain name. More than one SLD can function on the same IP Address.[3]
ccSLDs
A ccSLD, or Country Code Second Level Domain, refers to when an additional prefix is added to a ccTLD. An example of this would be .co.uk, where .uk is the (cc)TLD and .uk is the (cc)SLD. In this circumstance, the domain name ("example" in "example.co.uk") would be considered the third level domain, as it is in the third position.[4] This can become confusing, as the domain name is commonly equated with the second level domain, and the subdomain is commonly equated with the third level domain. In these circumstances, the third level domain is sometimes referred to as a functional SLD.[5]