Rectangle

A rectangle is a 4 sided shape with 4 corners in which each side is straight and equal to the opposite side (in other words 2 sets of opposing equal sides). It also has 4 right angle corners. Rectangles usually occur naturally in living things which tend to be more round. Occasionally one might find a hard non-living substance like a rock which by chance happens to be rectangular. However, rectangles are usually man made. They have been known to humans since ancient times and were used in architecture because walls of buildings were often rectangular. Also writing tablets were often rectangular.
The ring pictured above is rectangular in shape. See Metal Jewelry Shaper to see jewelry of various shapes.