What exactly is a LOB index object?

This question was answered by Tom Kyte in an old post from 2001.


A LOB is simply a pointer. It points to an index. The index points to the chunks that make up the LOB.
Hence when you create a LOB, you will always get a lob index created (to find the chunks for the LOB fast) and a segment that holds the LOB data (chunks).

and

You control the placement of the LOB segment. You have NO control over the LOB index, it is an internal structure and goes where it goes. The LOB index is considered "part of the LOB" itself.