All forums using vBulletin use tags so most of the information below applies directly to other websites as well...
Tags are keywords that are added to threads so the information is categorized for searching purposes within the bulletin board community. Without proper tags it makes finding specific topical information more difficult.
Tags are displayed while viewing a Forum page, and also when viewing a specific thread. To view the tag's content while viewing a Forum, just hover the mouse over the blue 'tag icon' (without clicking).
Tags are hyperlinked. If you click a tag, which is displayed at the bottom left-side of all threads, you will then be directed to the page which displays all
of the threads identified with that particular tag.
Tags should always be directed at the main topics of the post or thread discussion.
You may add up to (5) tags to a thread you create (either at the time of posting or later on), or to someone else's thread.
You always have the option to go back and add more tags to a thread, or to delete tags that you've previously added (say for instance you've misspelled your tag-- this happens!).
Adding tags is helpful for the forum community.
The option to add Tags appears at the bottom right-side of all threads.
Just click "Edit Tags" and start typing. Or, you may choose to add tags at the time you create your own thread.
The goal is to not create your own tag if one already exists which is similar.
Also, try not to make the tag so obscure that you'll be the only one in the world to do a "tag search" for it
(everyone can search for tags using the Search capability at the top of every page). For example, probably nobody is ever going to do a tag search for "bicuspid" except of course if this was a dentistry forum.
If you want to add tag a post with 'rowing a boat', when you start typing (after clicking "Edit Tags"), 'rowing' may suddenly appear in the box. It's better to select "rowing" by clicking on it, then saving this, rather than continuing to type to create your own 'rowing a boat'. But it really depends, and it's your choice what you think is best. Note: if 'rowing' does not appear as you begin to type, assuredly there is no "rowing" OR "rowing a boat" already in the tag database (cloud).
By following this protocol and advice, ALL the threads tagged "rowing" will appear under the same tag category, making it more likely
that your tagged thread will be found when someone is searching for topical information.
Here's the "Tag Cloud" which will show you the Top 70 Tags already used by FitDay members:
FitDay Discussion Boards - Tags