Dear Raghu, OBC - NCL is for those candidates whose annual income for the entire family from all means falls beliw 8 lakhs per annum. NCL stands for non creamy layer. OBC has a certain reservation in NEET. In OBC sub category, OBC-NCL has certain benefits. So when you select OBC-NCL as your category, you are entitled to reservation. And if you qualify in NEET and when you appear for counselling because you benefitted from OBC-NCL as your category, you are supposed to submit the proof of OBC-NCL certificate for authentication purposes. Suppose you do not belong to OBC-NCL but you selected OBC-NCL as your category for whatsoever reasons and during the counselling if you do not submit the proof, it will be considered as malpractise and an incident of fraud.