Low poly (short for Low Polygon) is a term used for polygonal mesh models that have a reduced number of polygons (also referred to as facets, triangles, or faces) compared to other models. For example, here is a mesh model of a sphere, composed entirely of triangles.

As you can see, the difference in the number of triangles used makes a big difference in the appearance as well as the file size of a part. 

Using the 3D Low Poly Generator website, you can reduce the number of polygons on a 3D model and make your own low poly masterpiece, no 3D modeling experience required!