Bell Jar – noun
a bell-shaped usually glass vessel designed to cover objects or to contain gases or a vacuum
http://www.thefreedictionary.com/bell+jar
The Bell Jar – Sylvia Plath
“wherever I sat—on the deck of a ship or at a street café in Paris or Bangkok—I would be sitting under the same glass bell jar, stewing in my own sour air”
Throughout this story the significance of the bell jar was very important here we see Esther feeling that she is inside of a bell jar because she is suffocating within her own thoughts. Esther is not able to express what she truly feels in this is why she feels trap.