The overall comfort of people (health, education, food, transport, etc).
A common measurement is GDP per capita, where we divide the region's gross domestic product (GDP) by how many people.
Another way is to use the Human Development Index (HDI), which uses many factors such as education level, life expectancy, etc.
Example: Sam accepted a job with a lower salary, because the area had better public transport and health care, which lifted the Standard of Living.