Communication Ethics book part for Annotation. (This is an automatically generated summary to avoid having huge posts on this page. Click through to read this post.)

In the context of web pages, annotation refers to the practice of using some software program to leave notes on web pages that others using the same program can view. (Note that if only the author can view the notes, it doesn't matter.) Perhaps the most famous example of this is the now-defunct Third Voice, which no longer exists even as a website I can point you to, only the odd screen shot here and there.

Third Voice screen shot, from here. One note is opened, "Is it art?". Another note is attached to "Photos & Images". In the upper left corner you see the Third Voice control panel. If I remember correctly, and based on the "More notes on Visual Arts" part that's cut off, this was one of Third Voice's "official" conversation threads, which they would feature on their home page in an attempt to encourage people to use the software for discussing various things, such as the given topic here.
A screenshot of Third Voice on the White House web site, during the Clinton Administration. Unsurprisingly, the White House site was one of the more active ones. This is a later version of the software, which added threading capabilities to the message (you can see the "Al Gore 2000" thread opened on the left), and the hint of the ability to have a distinction between "Public" and "Private" notes, which, to the best of my knowledge, was never implemented, at least not publically.

It is instructive to take a look at how Third Voice and related software accomplish this technically, because it is a paradigmatic example of how to effect large-scale integrity attacks. Despite the demise of Third Voice, other software still exists which has similar capabilities.