The Subset, in a general sense, is a set whose elements are all contained within another, larger set. In the context of computing and software, the term often refers to a simplified or limited version of a larger specification, program, or library. A subset implementation includes only a portion of the features of the full version. This is often done to reduce complexity, decrease memory footprint, or target a specific use case.
For example, an embedded microcontroller with limited memory might run a "subset" of the full TCP/IP networking stack, implementing only the essential protocols needed for basic communication and omitting more advanced features. Similarly, a manufacturer of a low-cost programmable power supply might claim that it is "SCPI-compliant" but only implement a subset of the full SCPI command set--perhaps just the core commands for setting and measuring voltage and current, while leaving out more complex commands for triggering or list mode operation. When working with such a device, a programmer must consult its documentation carefully to understand exactly which commands from the standard are supported and which are not. Using a subset can be an effective engineering trade-off, providing necessary functionality while minimizing resource requirements and development costs.