Points out the section where an entry in index_phash belongs.
The phash of the indexed document.
The phash of the "parent" TYPO3 page of the indexed document.
If the "document" being indexed is a TYPO3 page, then phash and phash_t3 are the same.
But if the document is an external file (PDF, Word etc) which are found as a LINK on a TYPO3 page, then this phash_t3 points to the phash of that TYPO3 page. Normally it goes like this when indexing: 1) The TYPO3 document is indexed (this has a phash-value of course), then 2) if any external files are found on the page, they are indexed as well AND their phash_t3 will become the phash of the TYPO3 page they were on.
The significance of this value is that indexed external files may have more than one record in "index_section" (with the same phash), a record for each parent page where a link to the document was found! There are details about this in the section of this document that describes the complexities of indexing pages.
The id of the root-page of the site.
The id of the level-1 page (if any) of the indexed page.
The id of the level-2 page (if any) of the indexed page.
The page id of the indexed page.
This is just an autoincremented unique, primary key. Generally not used (i think)