This drove me up the wall, until I researched it.

A document can be viewed as an object with a set of pointers to the words it contains.

The inverse of that, was a word object, with a list of pointers to the documents it is found it. This was referred to an an inverted DOCUMENT index. This is what people would normally just call an index.

At some point, people dropped the "DOCUMENT" part, and started just calling it an "inverted index". This makes no sense, grammatically, as it's the document that is inverted, not the index, but it is what it is.

So, an inverted index is just an index.

Wow, thanks for the explanation! That was driving me nuts too, as I was waiting for the point where they would invert the thing they built and what that would look like, though that point never came. But now I don't need to put in the time that you did!

In summary, they are not "inverted index" in the sense of "the inversion of what you'd normally think of as an index" but instead in the sense of "a map which provides the inversion of the map from documents to words in them, in other words, an index".

Love this take.