> The primary distinguishing characteristic of systems programming when compared to application programming is that application programming aims to produce software which provides services to the user directly (e.g. word processor), whereas systems programming aims to produce software and software platforms which *provide services to other software*, are performance constrained, or both (e.g. operating systems, computational science applications, game engines, industrial automation, and software as a service applications).
https://en.wikipedia.org/wiki/Systems_programming
> The primary distinguishing characteristic of systems programming when compared to application programming is that application programming aims to produce software which provides services to the user directly (e.g. word processor), whereas systems programming aims to produce software and software platforms which *provide services to other software*, are performance constrained, or both (e.g. operating systems, computational science applications, game engines, industrial automation, and software as a service applications).