hreflangxdefault
hreflangxdefault is a term used to describe the use of the hreflang attribute value x-default in link rel="alternate" annotations across a multilingual site. It designates the default page to show when no language or regional match exists for a user’s query or locale.
In practice, x-default is not a language code; it is a special value recognized by search engines.
Implementation involves including, on each set of language pages, an x-default link alongside reciprocal hreflang entries
Best practices encourage using x-default for the main landing page or a language selector page, and including
SEO considerations note that major search engines, including Google, support hreflang with x-default and use it
Historically, x-default was introduced to provide a non-targeted option within multilingual markup, and the term hreflangxdefault