导体由普通状态向超导态转变时的温度称为超导体的转变温度，或临界温度，用Tc （Critical temperature）表示．

In physical chemistry, thermodynamics, chemistry and condensed matter physics, a critical point, also called a critical state, specifies the conditions (temperature, pressure and sometimes composition) at which a phase boundary ceases to exist. There are multiple types of critical points such as vapor–liquid critical points and liquid–liquid critical points.