what is fee waivier and is it depend on obc/sc/st ranking ???

Dear Abhishek
You can find this helpful.
It is a general term to say "you don't have to pay the tuition fee". e.g in the US, the waiver may be because you have good scores in lets say SAT, GRE, GMAT etc. when you are enrolling to undergraduate or graduate programs. Some students get Assistantship(teaching, research etc.) instead of the tuition waiver where the student needs to work or help the professor, teach undergrads etc. for a minimum number hours per week so they get some money towards assistantship. Tuition waiver sometimes is also referred to financial aid.
Likewise above, we are having that in B-Tech too. It's not depends upon the caste but it depends on the merit/marks/percentage. Only few colleges may have this option.
All the best.

Fee wavier means you will have to pay less for that very course,for eg if you have to give 20000 in private and 5000 in government then any TFW students(if got that seat) will give 4000.