Reverse index

As far as I understand it, it's just the index with the sort of classification as opposed to what is natural, that is, from the highest to the lowest. I may be mistaken for lack of a larger context where the term is being used. It is used when it needs just this characteristic. It has nothing special in its structure, only the data is treated differently (the number of any kind is denied and the string suffers a little manipulation in its characters according to collate ).

Inverted index

If I understand what is in the question, it is an index where you have several values pointed out, which is not normal.

This is very used in textual search, so you search for words, the index finds the word and there are all places where the word is contained.

In some cases the index may have more information to improve the search, such as placing the place where the information is, its weight, etc.