OPT is a benefit authorized by US Citizenship and Immigration Services (USCIS) that extends the F-1 student status to allow you to work in the U.S.A. in order to gain practical training in your major field of study.
There are two types of OPT visas:
Only students pursuing a degree (Bachelors, Masters and Doctoral degree programs) are allowed to apply for an OPT. Students who have graduated from a US College or University with a specific degree in the STEM fields (Science, Technology, Engineering, Mathematics) can apply to extend their OPT. In this case, they can extend it for an additional 17 months.
Note that students on OPT must report their jobs to the international office at their university. Most international offices have an interface for students to report and update their job details online.