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.
Variations that add different types of blurriness. Unlike blur transforms, they do not ignore their inputs or create shapes by themselves. Most are best used in conjunction with other variations on the same transform, although a few have an incorporated linear so this is not needed.