I think that "de-indexing" means being removed from the index, and "re-indexing" is being put back in it again. Was there any particular context to this question? Cryo.
every time google finds new content it will re-index all your content if web site is not present for some days or broken links u get negetative points then after some time still not active then even google will remove website from cache that is de-indexing.