Year 1 Ponies refer to My Little Pony versions that were released in the first year of G1 production, which was 1982-1983. All of the ponies released in Year 1 were Earth Ponies.
Year 1 Ponies include Blossom, Blue Belle, Butterscotch, Cotton Candy, Minty, and Snuzzle. These first releases had flat feet, so they're often referred to as Flat Foot ponies. Later releases of these same ponies had concave feet.