Digital Infrastructure
The SDIA defines digital infrastructure as follows:
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.

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.