Think of tags as like a book index where you find words and which pages they are on, the same principle applies here. Although it's taken a stage further so it might not be the word, but the subject, so for example if you're looking for things to do with fractal gradients for example. A tag may bring back posts with gradient files, as well as posts that discuss gradients, or tutorials about them.
Posts tagged as black
Peek a Boo Fractal Gradients
By Nancy Pierce You’ll find 14 of what I call ‘peek-a-boo’ gradients in … Details
Black & White Maurer_lines – Webby Frame
My 2nd Submission to the Black & White Maurer lines Flame Game…
This is I named : Webby Frame