In the United States UXO, as defined in 10 USC 101(e)(5), is one of three categories of military munitions that may pose unique explosives safety risks that fall under the broader term "Munitions and Explosives of Concern" (MEC). The other two categories of MEC are Discarded Military Munitions (DMM), as defined in 10 USC 2710(e)(2) and Munitions Constituents or MC (e.g., TNT, RDX), as defined in 10 USC 2710(e)(3), that is present in high enough concentrations to pose an explosive hazard.