core + attic (Attic Area): these terms have been either deprecated from the core or extentions, or removed from pending as not accepted into the full vocabulary.

relatedLink

Canonical URL: http://schema.org/relatedLink

Thing > Property > relatedLink

A link related to this web page, for example to other related web pages.

Usage: Between 10,000 and 50,000 domains
Values expected to be one of these types
URL
Used on these types
WebPage

Schema Version 3.4