Charles Wang, Data Scientist at Noodle Education
From the IPEDS (Integrated Postsecondary Education Data Set) data dictionary, which was used to help build the Finance section:
"Income level - The income that was used by the institution’s financial aid office to determine the student’s Expected Family Contribution (EFC). For dependent students this will include the parents’ adjusted gross income and the student’s adjusted gross income. For independent students this will include the student’s adjusted gross income."
In short: adjusted gross income.