Precipitation, in the simplest terms, is the process by which water, contained in the clouds, falls down under the influence of gravity. There are several forms of precipitation, including rain, snow, hail, sleet, drizzle, freezing rain, etc. Among these forms, rain and drizzle are the only precipitation types that deliver liquid water; all others cause frozen water to fall down on the ground.
Rainfall is the most common form of precipitation and occurs when water droplets grow to a size of 0.5 mm or more. Rainfall can be very light, moderate, or very heavy (resulting in flooding).
If the size of the droplet is less than 0.5 mm, the precipitation is called drizzle.
Snow is the precipitation in the form of solid, frozen water. Snow is formed when the temperature is below freezing and falls down to the surface. If the temperature in the atmosphere is not sufficient to melt the snow, we receive snowfall.
Hail is commonly observed during thunderstorms and consists of very large pieces of ice (5 mm or larger).
Sleet occurs when snow partially melts during its fall through warm layers and it refreezes when the drops fall through freezing conditions. Thus, hail is the precipitation in which we receive snow pellets.
Freezing rain happens when supercooled water droplets fall on surfaces that have freezing temperatures. This causes the water to freeze on the surfaces, such as roads, pavements, cars, etc.
Hope this helps.