Obviously there no one definition, but this one by Cambridge Centre for Smart Infrastructure and Construction covers the essence of smart infrastructure.
In a world where infrastructure is truly smart, sensing technologies are embedded in infrastructure and the equipment it interacts with. These sensors are connected to a communication backbone which allows real-time data acquisition and analysis. The information gathered is analysed, interpreted and delivered as reliable, robust and meaningful information to infrastructure providers, who can then make better-informed decisions about the structural health and maintenance of their assets.
In a sensing environment, infrastructure is able to respond in real time to users’ needs. Self-aware infrastructure assets direct their own maintenance, leading to condition-based maintenance, reduced down time and greater operational efficiency of the infrastructure overall.
Better information leads to an enhanced understanding of the behaviour of infrastructure. The impact of this will lead to transformations in the approaches to design and construction as well as step changes in improved health and productivity, greater efficiency in design and performance, a low-carbon society and sustainable urban planning and management.
Definition by CSIC.
Other terms used are: Structural Health Monitoring (The International Society for Structural Health Monitoring of Intelligent Infrastructure = ISHMII) or Prognostics and Health Management (PHM Society).