"after this adjustment" refers to the salary after a cost-of-living adjustment has been carried out on it. It is still a "salary", it is not the same as "income after all expenses".
Someone has carried out an "adjustment" to the salaries, which, while I don't know exactly what they've done, probably means that the salaries have been changed to fit a standard cost of living. So you can see it as being the salary they would have in a place where the cost of living is "standard", that would allow them to live the same lifestyle.
The full adjustment is probably reasonably complicated, and could be done in different ways, but as a toy example we could adjust a salary to account for rent differences. It mentions that monthly rent for a one-bedroom apartment in San Francisco is $3000 a month, while the national average is $1200 a month. So to adjust for the difference in the average rent, you could decrease the salary of a San Franciscan by $1800 a month to find the equivalent salary in a place with the national average rent cost. A real-world salary of $100,000 in San Francisco would therefore be changed to a salary of $78,400 after adjustment (100,000 - 12 * 1800).
To summarise, it is the equivalent salary if you normalise to account for the difference in how much goods and services cost locally.
For info, here is the Wikipedia article on cost of living: https://en.wikipedia.org/wiki/Cost_of_living