Definition of backlink:
(n) :
(Internet) A hyperlink to a webpage from an external website.
(n) :
(computing) A link to another page that links to the current one, often in an automatically assembled list of links to all other such pages, allowing for bidirectional navigation.
(n) :
(computing) A reference to an object on another server, allowing it to be updated periodically.
(v) :
(Internet) To link in this fashion.