neutrons that have not been slowed down and have reached equilibrium with matter at room temperature
Thermal neutrons are a class of Neutron which are said to be in 'thermodynamic equilibrium' which means they are moving with the same kinetic as their surroundings. At room temperature the average energy of a thermal neutron is around 0.025 eV . Their significance in Radiation Protection is quite different to that of Fast Neutrons .