Neutrons of kinetic energy less than some specified value. This value may vary over a wide range and depends on the application. In reactor physics, the value is frequently chosen to be 1 eV; in dosimetry, the effective cadmium cut-off is used.
Source:
PAC, 1982, 54, 1533. 'Glossary of terms used in nuclear analytical chemistry (Provisional)' on page 1547 (https://doi.org/10.1351/pac198254081533)