A bell jar, also known as a cloche or display dome, is a bell-shaped vessel made usually of glass and sometimes of plastic and designed to cover objects or contain gases or a vacuum. These objects have various purposes. In a household setting, they were normally used as a protective dust cover for the object covered by it. In a lab setting, they were used to trap gasses or vacuums within the container, in this setting they're specifically referred to as a bell jar. In an agricultural setting, they were used to cover outdoor plants to protect them from frost, in this setting they're specifically referred to as a cloche.
A bell jar may or may not have a knob at the top to serve as a handle when picking it up.
