The combination of a particular computer and a particular operating system WordNet 3.0 & Open English WordNet

A computing platform, digital platform, or software platform is an environment in which software is executed. Wikipedia

The environment in which a piece of software is executed Wikipedia Disambiguation

A framework on which applications may be run Wikipedia Disambiguation

Hardware architecture and/or software framework Wikidata

The combination of a particular computer and a particular operating system. OmegaWiki

A particular type of operating system or environment such as a database or other specific software, and/or a particular type of computer or microprocessor, used to describe a particular environment for running other software, or for defining a specific software or hardware environment for discussion purposes. Wiktionary

Computing: particular type of operating system or environment. Wiktionary (translation)