1. Equipment that has imprecise characteristics that do not meet system reliability requirements.
2. In military communications, equipment that has insufficiently exacting characteristics to permit its use in trunks or links.
Note: Low-performance equipment may be used in loops if it meets loop performance requirements.
3. Tactical ground and airborne equipment that (a) has size, weight, and complexity characteristics that must be kept to a minimum and (b) is used in systems that have components with similar minimum performance characteristics.
Source: from Federal Standard 1037C and from MIL-STD-188