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 based on polynomial Julia sets. For escape time fractals, the formula is z → z^n + c. For flames, the mapping is reversed and the “+ c” part is done by the affine transform, so these variations basically take the root of the input taken as a complex number, returning one of the results at random.