NEET is the entrance examination for admission to MBBS,BDS, Ayush and Veterinary courses across India. So to be eligible for NEET, you should have completed your 12th, passed in all subjects and secure a minimum aggregate of 50% in Physics, Chemistry and Biology. It is 50% for General Category, 45% for PWD and 40% for OBC,SC,ST. Now if you belong to OBC Category, the Category you belong to should be also listed in the Central OBC list. Or else you will be considered as General Category and so you have to secure a minimum aggregate of 50% in Physics, Chemistry and Biology. This 50% is inclusive of the Theory and Practical marks scored in Physics, Chemistry and Biology collectively. You needn't score 50% in Physics, 50% in Chemistry and 50% in Biology separately. You need an aggregate of 50% or 40% depending on your Category as an aggregate in Physics, Chemistry and Biology. And along with Physics, Chemistry and Biology, you should also have studied English as one of the core subjects in your 12th.

On the other hand IMAT stnds for International Admissions Test that is the admission test for studying Medicine in Italian Universities. IMAT has 4 sections and they are:

Logical Reasoning and General Knowledge

Scientific Knowledge from Biology, Chemistry, Physics and Mathematics at School level. You can check the complete information at their official website: https://www.admissionstesting.org/for-test-takers/imat/about-imat/ . And NEET is also mandatory to study MBBS abroad. So even if you appear for IMAT, you should still appear for NEET and qualify in NEET to study MBBS in any of the Foreign Universities.