Curricular Practical Training or "internship", is a work opportunity/experience for pay directly related to your studies that can be authorized during your academic program.
Immigration regulations state that:
Curricular Practical Training is intended to be an important part of an educational program. It is not to be seen or used as a convenient means to circumvent employment restrictions.
You must be in valid F-1 status and have been enrolled full-time for one full academic year (9 consecutive months for students on the semester system, 2 trimesters for GSM students). Enrollment in intensive English studies does not count toward time in status.
The internship course must be 1) an important and integral part of your program of study; 2) be listed in the catalog for credit; and 3) be approved by an appropriate faculty member or department chairman.
Part-time CPT is not limited and does not impact OPT. However, an accumulation of 12 months of full-time CPT eliminates OPT.
CPT does not alter full-time enrollment requirements. When enrolled full-time, you may work only part-time - 20 hours per week. (Generally speaking, you will not be permitted to work part-time on campus while engaged in part-time curricular practical training.)
Full-time CPT (more than 20 hours per week) is permitted during vacations or when you are enrolled less than full-time as during a vacation or in your final term. Under very limited special circumstances full-time CPT may be authorized during full-time enrollment.
CPT authorization is done through SEVIS, the federal government data base, for a specified employer at a specified location for a specified period of time.