Open states are those states which offers admission to the course to any qualified student all over India. Closed states are those states which don't allow to participate other state students to there state. This is the difference between the two. If you want to go out of your state and want to study the course in some medical college in other state then you have to go for the open states as they allow the students from other states to participate in the counselling.

To know more about NEET counselling visit the link below:

https://medicine.careers360.com/articles/neet-counselling

I hope this answer helps. All the very best for your future endeavors!