Hello

I think it means your roll number. You can call the helpline if you are still in doubt

Help Line No. for Form Filling: 9326552525

E-mail Address for Form Filling:- lawquery@mkcl.org.

You can go through the guidelines to be sure http://www.mahacet.org/cetcell/wp-content/uploads/2017/02/Information-Brochure-CAP-LL.B-3-Yrs.-2017-Final-Copy_Dt-21-06-2017.pdf . All the best.