What does F2 mean for U.S. immigration?

Is an immigration category

(F1) First preference: unmarried adult children of U.S. citizens and their minor children (if any).

(F2) Second preference: spouses, minor children, and unmarried adult children of legal permanent residents.

Note: At least 77% of the visas available to such priority applicants must be given to spouses and minor children, and the remaining quota is allocated to unmarried adult children.

(F3) Third preference: married children of U.S. citizens, and their spouses and minor children.

(F4) Fourth preference: brothers and sisters of U.S. citizens, and their spouses and minor children, if the U.S. citizen is 21 years of age or older.

For a family of three, it depends on the relationship between the respondent and the American applicant. The relationship is as above