I like to think of infrastructure as everything from wall jack to wall jack. Thinking of infrastructure in this manner enables effective conversations with those who are less familiar with the various components.
The term IT infrastructure is defined in ITIL as a combined set of hardware, software, networks, facilities, etc. (including all of the information technology related equipment) used to develop, test, deliver, monitor, control, or support IT services. Associated people, processes, and documentation are not part of IT Infrastructure.