Optional Practical Training (OPT) is for undergraduate or graduate students who have completed or are near completing a degree in an academic institution in the United States. The OPT is designed to complement college studies with practical training. This means the job has to be related to the student’s college major. It is valid for one year and it’s done under an F-1 or M-1 status.
There are several differences with a work visa, including the period of validity, the kind of jobs you may perform, the fact that work visas are tied with a specific employer while the OPT is not, among others.
For more information about OPT, click here.