the study and practice of reducing IT's environmental impact as well as using IT as a tool for improving sustainability in other areas (usually in the context of a business).
Green IT is the study and practice of reducing the environmental impact of IT and/or using IT as a tool for improving sustainability in other areas (usually in the context of a business).
Reducing IT's impact is sometimes also referred to as Green IT 1.0, whereas using IT to improve sustainability is also known as Green IT 2.0. or as IT for Green. Other names for Green IT include green computing, sustainable computing, or ICT sustainability.
Green IT includes "the study and practice of designing, manufacturing, using, and disposing of computers, servers, and associated subsystems - such as monitors, printers, storage devices, and networking and communications systems - efficiently and effectively with minimal or no impact on the environment." (as defined by San Murugesan)