Confluence, at its base, was built on the principle of a Wiki.

A Wiki or wiki (pronounced "wicky" or "weekee", see pronunciation section below) is a website (or other hypertext document collection) that allows a user to add content, as on an Internet forum, but also allows that content to be edited by any other user. (http://en.wikipedia.org/wiki/Wiki)

Like many other wikis, Confluence offers:

It allows rapid commenting and overview of textual information by large groups of users.

How is Confluence useful?

Confluence lets large groups of users create and edit information together. It includes added functionality which other knowledge management tools do not possess.