Auto-linking
From MoodleDocs
Auto-linking a feature of Moodle by which words or phrases used within a Moodle site are automatically linked (by highlighting in grey by default) if there is a content page (or resource or activity) within the site with the same name.
Autolinking can be globally switched on/off in a site's setting, and specific links can be prevented by adding <nolink> ... </nolink> tags around the relevant content in HTML markup mode.