OPT is an acronym for Optional Practical Training. The F-1 student visa allows an international student to enter US and attend the academic program they have enrolled in. All F-1 visa holders are entitled to pursue work for a limited period in order to apply their knowledge gained in the classroom to real world situations. 
To be eligible for Optional Practical Training, students should:

• be enrolled in a full time academic program for a duration of one year preceding the submission of OPT application.

• maintain a valid F-1 status.

• and intend to work in a field related to the program of study.

The Optional Practical Training facility is offered by the US Citizenship and Immigration Services {USCIS}. The OPT is valid for a period of 12 months. Students can either use the 12 months during the course of studies or use the entire period

after the completion of their graduate program. The OPT application of a student takes about 90 to 120 days to process. Students should therefore make their application at the earliest possible time.

Since one of the requirements of the OPT is that an applicant should have at least one year of academic study behind him, students should submit the OPT applications to their respective University offices at least 90 days (3 months), before the completion of their first academic year. The OPT card is approved with a specific beginning and end dates. These dates are to be specified by the students. 

Students must be enrolled for an academic course for one academic year to apply.   Students are eligible for 12 months of OPT per academic level, that is undergraduate, graduate, PhD.  In addition, STEM streams (Science, Technology, Engineering and Mathematics) are eligible for a 17-month extension in addition to the 12 months available to all students. 

Application for OPT can be made 90 days before the program end date and within 60 days from the end of the program.  It is important to apply early for OPT.  Applications are processed by the U.S. Citizenship and Immigration Services (USCIS) and generally take 3 months to receive the Employment Authorization Document (EAD).

It is important to note that you do not need to have a job to apply for a OPT.  You can apply for an OPT while actively seeking employment, but however, you cannot be unemployed for more than 90 days while on OPT.  In other words, if you are unemployed while on OPT, ensure that you find a job within 90 days of beginning your OPT.

The International Student Services Center and the Career Planning Center at the University will have more information in this regard.