Imagine drawing a circle on a piece of paper with a dot in the middle. Now, draw lines from the dot to the circle, like the spokes on a bicycle wheel. These lines are called "radials."
A radial set is just a collection of these lines, arranged in a specific way. For example, you might have a radial set where every line is evenly spaced, or where the lines are all the same length.
Radial sets can be found all throughout nature, like in the petals of a flower or the scales of a pineapple. People also use radial sets in art and design, like creating patterns on a quilt or arranging the spokes on a bicycle wheel for optimal performance.