Extra rendered content or keywords

Drupal 7 with Apache Solr Search. One can set biases to to be used by Apache Solr Search in sorting search results.  Most of the controls are self explanatory.  However, “Extra rendered content or keywords” seems vague. When editing a, for example, basic page, just where is this extra rendered content or keywords found?  Thank you.

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Source: https://www.drupal.org/taxonomy/term/22/feed