The term thermal diode is sometimes used for a (possibly non-electrical) device which causes heat to flow preferentially in one direction. Or, the term may be used to describe an electrical (semiconductor) diode in reference to a thermal effect or function. Or the term may be used to describe both situations, where an electrical diode is used as a heat-pump or thermoelectric cooler.
Read more about Thermal Diode: Introduction, One-way Heat-flow, Electrical Diode Thermal Effect or Function, Thermoelectric Heat-pump or Cooler, Advancements