They are geometrical forms which are said to act as a template from which all life springs. They are named after the ancient Greek philosopher Plato. To the Greeks, these solids symbolized fire, earth, air, spirit (or ether) and water.
This pin is similar to the first pin, it has those fine white lines that show the proportion of the bird. I like how it shows the original image and then it transforms into a pixelated bird. Low poly, looks like a fun or frustrating exercise to do.