Sustainable urbanism is:
Sustainable Urbanism, as a defined term, is application of sustainability and resilient principles to the design, planning, and administration/operation of cities. There are a range of organizations promoting and researching sustainable urbanism practices including governmental agencies, non-governmental organizations, professional associations, and professional enterprises around the world. Related to sustainable urbanism is the Ecocity movement (also known as Ecological Urbanism) which specifically is looking to make cities based on ecological principles, and the Resilient Cities movement addresses depleting resources by creating distributed local resources to replace global supply chain in case of major disruption. Green urbanism is another common term for sustainable urbanism. Sustainable development is a general term for both making both urban and economic growth more sustainable, but isn't specifically a mode of urbanism.
Sustainable urbanism aims to close the loop by eliminating environmental impact of urban development by providing all resources locally. It looks at the full life cycle of the products to make sure that everything is made sustainably, and sustainable urbanism also brings things like electricity and food production into the city. This means that literally everything that the town or city needs is right there making it truly self-sufficient and sustainable.
The architect and urban planner Doug Farr discusses making cities walkable, along with combining elements of ecological urbanism, sustainable urban infrastructure, and new urbanism, and goes beyond them to close the loop on resource use and bring everything into the city or town. It is about increasing the quality of life by bringing more resources within a short distance and also increasing the quality of products that are offered.