Hello,

Correspondence course usually means distance learning. You can study online and give exams.

Traditionally, this usually involved correspondence courses wherein the student corresponded with the school via mail or online classes.

You will receive alerts for assignment by mail and you can submit them online for grading.

Sol is part of delhi university open schooling where you do not have attend classes regularly and you can attend them on weekends.

https://university.careers360.com/articles/du-sol-admissions

You can know more here:

Lastly NCWEB, popularly known as Non-Collegiate Women's Education Board,  is for female students only.

Where in women students were enabled to take some of the examination of the University with special coaching but without attending regular classes. Its also the part of delhi university.

Hopefully this helps!!