In an onion, the edible part is the bulb. The bulb is essentially a modified stem that grows underground. It consists of thick, fleshy scales that store nutrients for the plant`s growth and development. These scales are what we commonly refer to as onion layers. The bulb is surrounded by a papery outer layer, which acts as a protective covering. The leaves of an onion are also edible, but they are usually less commonly consumed compared to the bulb. The stem of an onion is present above ground and helps in supporting the plant`s growth, but it is not typically consumed. The root of an onion is responsible for absorbing water and nutrients from the soil and is not the edible part of the plant.