thermal equilibrium

This term is a technical expression used primarily in thermodynamics and physics. It describes a specific state of stability where heat transfer ceases because temperatures have equalized. In a scientific context, it is used to describe the end result of the Zeroth Law of Thermodynamics.

Because it refers to a specific physical state or condition, it is treated as an uncountable noun. It is not used to describe a general feeling of balance, but rather a measurable physical property of systems in contact.