The Golden Ratio is a rectangle where if you make a square of one end of the rectangle, the remainder is a rectangle of the exact ratio as the first original rectangle.
short side is 0.618034 times the long side.
If you make consecutive squares in the consecutive remaining rectangles to infinity, or as small as you can go, you can draw a spiral from joining the arcs within each square, (from a corner) which if ironed out to remove the disparity from the changing radii, you can draw the golden spiral.
Used for hundreds ( or thousands) of years in some artistic cultures.
I calculated the number myself after reading about it, and drew the consecutive rectangles, then the spiral; very finnicky work, but looks good.
Most of my paintings are on Golden Ratio picture canvasses I made myself.