MIL-STD-1750A or 1750A is the formal definition of a 16-bit computer instruction set architecture (ISA), including both required and optional components, as described by the military standard document MIL-STD-1750A (1980).
In addition to the core ISA, the definition defines optional instructions, such as a FPU and MMU. Importantly, the standard does not define the implementation details of a 1750A processor.