There's a class of data structures where you preprocess some other data structure in order to answer queries about it more efficiently.
That includes trivial things like sorting/hashing, less trivial things like quad trees, and includes far less trivial things such as dominator trees, interval decompositions of DAGs or distributed data structures using labelings.
I was wondering what is a common term for such data structures, and if there isn't, how to describe them best. "index-like" comes to mind, but there aren't yet any tags with the word "index" here so it does not seem to be common.