An SLD (Second Level Domain) is a domain that is hierarchically directly below a TLD.
It is usually used as a way to differenciate various functions of a server or to delimit areas under the same domain. For example, www is a commonly used SLD to indicate the domain points to a web server.
As another example, in developer.mozilla.org, the developer SLD is used to specify that the subdomain contains the developer section of the mozilla website.
Pour en savoir plus
Culture générale
- SLD on Wikipedia