It's purely about the environment, or so many people think.
The definition of Sustainability on Dictionary.com is this: The quality of not being harmful to the environment or depleting natural resources, and thereby supporting long-term ecological balance.
The modern definition of Sustainability, though, is two-fold. Today's definition of Sustainability understands that the survival of the human race cannot be separated from the survival of the planet. And it strives to address both. These include factors such as poverty, health, peace, societal inequalities, along with more traditional ideas of climate action, responsible consumption of natural resources, and so on. It's all about creating a balance between needs of all people and the absolute need to protect the environment, by questioning the long term effects of our actions on future generations. The Earth Charter, defines it thus: "…sustainable global society is founded on respect for nature, universal human rights, economic justice, and a culture of peace."
According to Environmental Sciences.org, it is estimated that we use about 40% more resources every year than we can put back and that needs to change. Earth Overshoot day (If you haven't heard of it, find out more here.) comes early year after year. In 2017, it fell on August 2. That means that from August 2 2017 to December 31 2017, we were borrowing resources from 2018. We have to understand and accept that sustainability is a Universal responsibility. We need to figure out how to help ourselves, our families, the local communities, and other communities in need.