The term sustainability has been defined in many ways. The United Nations World Commission on Environment and Development defines sustainability in general terms as "development, which meets the needs of present generations without compromising the ability of future generations to meet their own needs." Another general definition is the capacity of a system to function effectively over time with minimum external input or the capacity of a system to endure over time. Many factors can be used to assess sustainability. Some that can be helpful to consider when assessing the sustainability of technologies or new media include: a) effectiveness, b) efficiency of services to optimize available resource usage and leverage demand and supply; c) financial viability; and d) equity, i.e., availability/ usability of media or technology for all populations (e.g. low tech ability, low bandwidth, etc.) d) reproducibility, such as integration and application in a variety of different settings; and e) portability, measured by ease of implementing and adapting concepts and approaches to other environments.