The Roll Number is present in the Hall ticket of your 10th and Graduation level. So in the hall ticket if you have serial number along with your registration number, then your board/university uses Roll Number to be the serial number.

Roll Number is a unique code assigned to each student to enlist them in examinations.

To know more about the SSC CGL, visit the link below:

https://competition.careers360.com/exams/ssc-cgl

I hope this answer helps. All the very best for your future endeavors!