What is a bulb?

The word "bulb" has several meanings, all of which refer, or originally referred, to an object with a round shape. There is no difference in pronunciation between these meanings.

In botany, a bulb is a short stem with fleshy leaves that act as food storage during dormancy. In photography, "bulb" is a camera setting that allows for long exposure times. An incandescent light bulb is an object that has a wire filament that, when heated, glows to provide light. A bulb is also an expanded part of a glass tube, such as the part forming the reservoir of a thermometer.