In 2010, the RFC “Defining Well-Known Uniform Resource Identifiers (URIs)” came out and suggested the prefix “/.well-known/” for so-called “known places” on the resource (site).
For example, if you follow the link https://github.com/.well-known/change-password, you will be redirected to a password change page. Safari in particular uses this: if it detects that your password is too weak, it will offer to change it.
Wikipedia lists the most common “.well-known” that can be provided by services:
To avoid conflicts, new proposed services must be registered with the IANA:
I especially recommend looking at security.txt