The DIESIS project  gives the following definition:
The Research Infrastructures part of the FP7 Capacities Programme supports an innovative way of conducting scientific research (referred to as e-Science) by the creation of a new environment for academic and industrial research in which virtual communities share, federate and exploit the collective
power of European scientific facilities.
The term e-Infrastructure refers to this new research environment in which all researchers – whether working in the context of their home institutions or in national or multinational scientific initiatives – have shared access to unique or distributed scientific facilities (including data, instruments, computing and communications), regardless of their type and location in the world.http://cordis.europa.eu/fp7/ict/e-infrastructure/home_en.html
It embraces networks, grids, data centers and collaborative environments, and can include supporting operations centers, service registries, single sign-on, certificate authorities, training and help-desk services.