From Joomla! Documentation
It contains usage information, categories and other content that is not part of the original template page.
To view the template page itself, see Template:NOINDEX.
This template adds __NOINDEX__, which may remove the page from some search engines and automatically categorizes pages in Category:Noindexed pages. By default, it displays no content.
|visible = yes – makes the template display a line of plain text to inform editors that the page is excluded from search engine indexing:
This page has been removed from search engines' indexes.
Note: to avoid unexpected results or unnecessary duplication, always wrap this template in:
Make sure you are familiar with the different ways noindexing is done.
__NOINDEX__ is disabled in
Category namespace and this template consequently has no effect there.
Note: major search engines should respect the NOINDEX tag, but it may take days or even weeks for content already indexed to be removed from them.
NOINDEX This template adds to a page, a search engine tag that prevents indexing Template parameters
|visible(When set to 'yes', the template will display a message stating that the page is not indexed.