Examines what software the server reports that it uses.
In the response from the web server, one of the headers it can set is the "server" header. This is used to describe the software that is used on the server. Disclosing the operating system and version is generally considered to be a bad idea as it can make it slightly easier for an attacker to target the server. However, disclosing the name and version of the server software (ex: apache or nginx) can help browsers work around bugs in certain versions.
For more information, please read the documentation on MDN Web Docs.