NEET is a National Eligibility cum Entrance Test conducted at both Unger graduate level, NEET-UG for admission in MBBS, BAMS, etc courses at graduate level after +2.
NEET-PG is a post graduate test for admission in Masters courses in medical field like MD, etc.
You could read more about them here:-
NEET is an entrance examination for admissions to various MBBA and BDS Colleges in India. The list of colleges accepting NEET, include both government and private colleges. It is for the students who wish to pursue education in medical fields. It is a three hour examination with maximum marks being 720.
For more details, please visit this link:
Hope this answer helps!