https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Set-Cookie
Domain=<domain-value> Optional
Specifies those hosts to which the cookie will be sent.
If not specified, defaults to the host portion of the current document location (but not including subdomains).
Contrary to earlier specifications, leading dots in domain names are ignored.
If a domain is specified, subdomains are always included.
Path=<path-value> Optional
Indicates a URL path that must exist in the requested resource before sending the Cookie header.
The %x2F ("/") character is interpreted as a directory separator and sub directories will be matched as well (e.g. path=/docs, "/docs", "/docs/Web/", or "/docs/Web/HTTP" will all be matched).
https://developer.mozilla.org/en-US/docs/Web/HTTP/Cookies
Scope of cookies
The Domain and Path directives define the scope of the cookie: what URLs the cookies should be sent to.
Domain specifies allowed hosts to receive the cookie.
If unspecified, it defaults to the host of the current document location, excluding subdomains.
If Domain is specified, then subdomains are always included.
For example, if Domain=mozilla.org is set, then cookies are included on subdomains like developer.mozilla.org.
Path indicates a URL path that must exist in the requested URL in order to send the Cookie header. The %x2F ("/") character is considered a directory separator, and subdirectories will match as well.
For example, if Path=/docs is set, these paths will match:
/docs/docs/Web//docs/Web/HTTP
subdomain
https://en.wikipedia.org/wiki/Subdomain
A subdomain is a domain that is part of a larger domain; the only domain that is not also a subdomain is the root domain.[1]
For example, west.example.com and east.example.com are subdomains of the example.com domain, which in turn is a subdomain of the com top-level domain (TLD).
A "subdomain" expresses relative dependence, not absolute dependence: for example, wikipedia.org comprises a subdomain of the org domain, and en.wikipedia.org comprises a subdomain of the domain wikipedia.org.