Which of the following terms is used in the field of economics ?

The barter system is one of the oldest methods of trade and commerce in human history, where goods and services are exchanged directly for other goods and services without the use of money. It is a system of trade based on mutual exchange. It is therefore related to economics. The other terms are not. Adiabatic is related to respiration(biology), Bohr theory and Plasma are related to particle physics.