Earth Ponies are ponies in the My Little Pony line that have a basic body shape without wings or horns like the pegasus and unicorn ponies. All of the ponies released in Year 1 were Earth Ponies, with other variations starting in Year 2.
The Year 1 Earth ponies had feet that were flat on the bottom (often called "Flat Foot" ponies), but starting in Year 2, all ponies had concave feet.