Annotation is the process of adding a layer of personal (with a potential for sharing) metadata on top of existing content such as highlights, notes, anchors etc.

Examples of exobrains 'Everything I know' wiki by Nikita Voloboev xxiivv by Devine Lu Linvega h0p3's Wiki Braindump by Jethro Kuan 'One Hundred Ideas for Computing' repository by Sam Squire more wiki examples from Nikita Voloboev