What is the X-Robots tag?

#2
The X-Robots-Tag can be used as an element of the HTTP header response for a given URL. Any directive that can be used in an robots meta tag can also bespecified as an X-Robots-Tag .
 
#3
The X-Robots-Tag can be used as an element of the HTTP header response for a given URL of the web page. It is Global, which means an X-Robots-Tag with HTTP responses allows you to specify crawling directives that are applied globally across a site.