From AMS Glossary
(Also called soft hail, graupel, tapioca snow.) Precipitation consisting of white, opaque, approximately round (sometimes conical) ice particles having a snowlike structure, and about 2–5 mm in diameter.
Snow pellets are crisp and easily crushed, differing in this respect from snow grains. They rebound when they fall on a hard surface and often break up. In most cases, snow pellets fall in shower form, often before or together with snow, and chiefly on occasions when the surface temperature is at or slightly below 0°C (32°F). It is formed as a result of accretion of supercooled droplets collected on what is initially a falling ice crystal (probably of the spatial aggregate type).