Here’s a list of ALL the registered tags. Click on a tag to see all the posts or pages having that tag assigned.
The tag cloud in the sidebar shows only the more popular ones and authors are encouraged to assign one relevant tag from that pool.
The # character is prepended to the actual tag name by the “hashtagger” plugin which also enables speedy tag assignment by typing a tag name as a hashtag in the title or body of a post or page. This ease is a bit risky and can allow the proliferation of singular tags so everyone is encouraged to use existing tags and, preferably, only those from the sidebar.