Definition for Digital infrastructure

The SDIA defines Digital infrastructure as

The total physical and software-based infrastructure necessary to deliver digital goods, products & services. This includes data centers, fiber infrastructure, server hardware, personnel, IT virtualization & infrastructure software, operating systems, etc.

Other definitions

In their paper “the digital entrepreneurial ecosystem” for the Small Business Economics journal, Susan and Acs define Digital Infrastructure (DI) as

Anchored in digital technologies, DI is a socially embedded mechanical system that includes technological and human components, network, systems, and processes which generate feedback loops that are self-reinforcing. [...] From an operational perspective, specifically information system service management, it is important that DI be treated as such. However, as infrastructure for a digital business model, DI should be considered as an interconnecting element of the digital business ecosystem. (Sussan & Acs, 2017)

Further elaboration on this topic can be found here.