Unexploded ordnance
Unexploded ordnance (UXO) means military munitions that have been primed, fused, armed, or otherwise prepared for action, and have been fired, dropped, launched, projected, or placed in such a manner as to constitute a hazard to operations, installation, personnel, or material and remain unexploded either by malfunction, design, or any other cause.
Source
40 CFR § 266.201
Scoping language
In addition to the definitions in 40 CFR 260.10, the following definitions apply to this subpart: