Onions are edible with a distinctive strong flavour and pungent odour which is mellowed by cooking. They generally have a papery outer skin over a fleshy, layered inner core. Used worldwide for culinary purposes, they come in a wide variety of forms including the small, delicately flavoured spring or salad onion.
Onions are frequently used in school science laboratories because they have particularly large cells which are easily visible through an optical microscope. See how to prepare an onion cell slide for details.