When I query the column, it seems to be arbitrary values from 1-60:
But the official documentation's description  doesn't explain how the values map to different enrollment types:
Level, full- and part-time status, degree-seeking/non degree-seeking status and year of study of student - This variable identifies the level of enrollment (unduplicated headcount) data for the institution. Enrollment counts are available by level of student (undergraduate or graduate). Undergraduate enrollments are disaggregated by degree-seeking and non-degree seeking status. Degree-seeking enrollments are further broken out by first-time, first year students, transfer-ins and continuing students. Undergraduate categories are available by full- and part-time status.
Undergraduate A student enrolled in a 4- or 5-year bachelor's degree program, an associate's degree program, or a vocational or technical program below the baccalaureate.
Degree/certificate-seeking students Students enrolled in courses for credit and recognized by the institution as seeking a degree, certificate, or other formal award. High school students also enrolled in postsecondary courses for credit are not considered degree/certificate-seeking.
First-time student (undergraduate) A student who has no prior postsecondary experience (except as noted below) attending any institution for the first time at the undergraduate level. This includes students enrolled in academic or occupational programs. It also includes students enrolled in the fall term who attended college for the first time in the prior summer term, and students who entered with advanced standing (college credits earned before graduation from high school).
Transfer-in student (undergraduate) A student entering the reporting institution for the first time but known to have previously attended a postsecondary institution at the same level. The student may transfer with or without credit.
Graduate student A student who holds a bachelor's degree or above and is taking courses at the postbaccalaureate level. These students may or may not be enrolled in graduate programs.
Full-time student Undergraduate: A student enrolled for 12 or more semester credits , or 12 or more quarter credits, or 24 or more clock hours a week each term. Graduate: A student enrolled for 9 or more semester credits, or 9 or more quarter credits, or a student involved in thesis or dissertation preparation that is considered full time by the institution. Doctor's degree - Professional practice - as defined by the institution.
Part-time student Undergraduate: A student enrolled for either less than 12 semester or quarter credits, or less than 24 clock hours a week each term. Graduate: A student enrolled for less than 9 semester or quarter credits