Key Reference and External Reference
These are some of the "lower" list fill in's regarding Joomla Meta information in content. Still worth some reasearch. I found the following
This is the reference that is used to pull the correct help information either from help files saved locally or on an online site like help.joomla.orgExternal Reference
Use this field to add a reference to an external resource that is relevant to this specific article. There is no global value for this field as it must be specific to each particular article.
Dave Huelsmann gives a great answer and he appears to know Joomla very very well.