Refers to sealed sources of radioactive material contained in a small volume (but not radioactively contaminated soils and bulk metals) in any one or more of the following conditions (taken from the NRC Orphan Source Initiative):

• In an uncontrolled condition that requires removal to protect public health and safety from a radiological threat;
• Controlled or uncontrolled, but for which a responsible party cannot be readily identified; Controlled, but the material's continued security cannot be assured. If held by a licensee, the licensee has few or no options for, or is incapable of providing for, the safe disposition of the material;
• In the possession of a person, not licenced to possess the material, who did not seek to possess the material; or
• In the possession of a state radiological protection programme for the sole purpose of mitigating a radiological threat because of one of the above conditions, and for which the state does not have a means to provide for the material's appropriate disposition.