I believe Cutoff is the Last Rank/Score which is called by CSIR for the Interview Process or for a Position as JRF/Scientist. While Qualifying Marks suggest the threshold to qualfy the exam and be eligible for the Rank list. For example 400 aspirants may have qualified the Examination, but for 60 Positions of JRF across CSIR Locations, the Regulatory Authority may choose 150 out of the 400 Qualified for Interview Process, with a comparatively lower cutoffs for OBC and Various Categories. So effectively you have a General Student with AIR 50 sitting beside an AIR 350 from SC Category for the Interview Process. Hence, doesnt mean the first 150 Candidates will be called for Interview, Rather it will be divided across Sections and Categories, each having a Different Cutoff.