What is the difference between : 'Kingdom Hearts Re: Chain Of Memories' and 'Kingdom Hearts 2: Final Mix +?

the difference is they are 2 different games one is the part of Sora's adventure in castle oblivion the other is a remake of kingdom hearts 2 with new boss fights and cutscenes as well as a limit mode and other features.as mentioned above both were released only in Japan at first but then re:chain of memories was released in other countries alone without final mix unlike in japan where they were bundled together.

Well, PS2s aren't region free, and since neither game was released in PAL...

Re:CoM is a full remake of the original CoM from the GBA to the PS2.
KH2FM+ is like a limited edition version of KH2 with all the extras that couldn't be included the first time around, including a Japanese version of Re:CoM (since it is JPN exclusive).

RE chains of memories is the gap between kh2 and kh1. kh2 final mix is just a spend off with added fights, secrets, boss, and places.

Final Mix+ is KH2 and Chain of Memories combined. Chain of memories is just that.

Like the others said, there different titles in kingdom hearts with different story modes.