The information system (IS) is the set of human, organizational and technical means that allow an organization to collect, store, process and share the information it needs to operate. It is not limited to IT: it also includes the processes and people who produce and use information.
Its technical side covers hardware, networks, software (ERP, CRM, business tools, email) and data. The department in charge of it is the IT department, led by a CIO.
In a large group, the IS is often a heterogeneous stack built over decades, with legacy applications that must coexist with the cloud and newer tools. Its security, its overall architecture and its cost are executive-level topics.
Why it matters when hiring
IS roles (CIO, enterprise architect, IS project manager, administrator) are not the same as product tech roles at a software vendor, even when titles look alike. A "developer" in a corporate IT department often integrates and maintains packaged software, while a startup developer builds a product. Clarifying this in the job ad avoids mismatched hires in both directions.