What It Is
Tagging adds specified search terms to your content and is another way of adding information to your content (photos, videos, blog posts, etc.) that will help people find it.
What It Does
When adding your photos or videos to sharing sites such as Flickr or YouTube, have a list of standard tags that will be used with all of your content – your company name and your core business. In addition, tag everything relevant to the specific content – the location, what’s happening, activities – anything that someone on the site might be searching for. Consider using alternate spellings or variations (kitten, kitty, cat) as well.
On Facebook tagging works a little differently – it allows you to notify people that you’ve flagged them in a note, a photo – even a status update. If you want to be sure a particular person sees something you’ve posted on Facebook, you can tag them. Two notes of caution – use this judiciously and remember that with the new profile, the most recent photos that people are tagged in will show up on their profile page
On Flickr, people attending the same event will often decide on a common tag and use that when sharing their photos. Then searching on that common tag will allow you to see all the photos from that event instead of having to search through separate photo albums or sets.
On YouTube, tags are also used to generate the “more like this” recommendations, so the more relevant tags you use, the more likely you are to show up as a recommended video.
What To Use It With
How To Use It
Tagging help – Flickr
Using Categories and Tags Effectively on Your Blog – Pro Blogger
Tagging Blogs Posts and Photos – About.com
Optimizing Titles, Tags & Text to Boost YouTube Traffic – Social Times
YouTube Video Tag Optimization – Search Engine Land