Everflux
Google’s database Index are updated at regular interval. Some times Google results started changing all through the month, in between the major updates. These change were known as everflux.

Expert document
A document that links to many other (same-topic) documents. Some search engines only consider links from expert documents - as opposed to all documents in the collection - when determining link popularity. According to the Hilltop paper, expert documents are "pages that have been created with the specific purpose of directing people towards resources".

Expert index
A special sub-collection within a search engine index. An expert index consists only of documents that are considered expert documents.