egit replacing single file - HEAD Revision vs File in git index

eclipse, egit, git, git-reset

Solution

`HEAD` is the version of the file that has already been committed.

The index is the version of the file that has been staged (added) in preparation for a commit, but not yet committed.

Problem

In the egit git eclipse plugin, I know I can "reset" a single file by right clicking on it and selecting Replace With > HEAD Revision. What is the difference between replacing with HEAD revision vs File in git index?

Original source