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.

harmonograph2

Harmonograph – Pendulum motion fractals

By Jesus Sosa From physics, we know the basic motion of a pendulum, the primary mechanism in the harmonograph machine, is sinusoidal. Both the x-axis and y-axis motion is delivered by pendulums, which means the basic equation for motion along each axis is a sinusoid.