The main page previously showed the name of the page as the heading. For example on https://nl.wiktionary.org/wiki/WikiWoordenboek:Hoofdpagina the heading of the page is "WikiWoordenboek:Hoofdpagina". This was problematic as the namespace is not always user friendly to newcomers.
Another common use case was hiding the main page heading via CSS inside MediaWiki:Common/Vector.css, however this also hid the heading on diff pages (see T38294). e.g.
A new change (T296969) allows more control/creativity over the text of the heading.
It is currently being used on Basque Wikipedia and MediaWiki.org
This change can also be used to hide the heading. To do this you can [[ https://it.wikipedia.org/w/index.php?title=MediaWiki:Mainpage-title-loggedin&oldid=124897087 | blank the heading message ]] and remove any CSS in MediaWiki:Common.css or Vector.css that was previously hiding it ([[ https://it.wikipedia.org/w/index.php?title=MediaWiki%3AVector.css&type=revision&diff=124911925&oldid=121630135 | example on Italian Wikipedia ]] ).
This is documented on https://meta.wikimedia.org/wiki/Small_wiki_toolkits/Starter_kit/Main_page_customization#Hide/change_the_text_of_the_header
Note, when blanking the header, this is currently supported only for the skins that the majority of our users use - Skin:Vector and Skin:Minerva (From 13th January [wmf17 release], this will also include Modern and Monobook). To remove the CSS from Common.css totally, you should add corresponding CSS to MediaWiki:Modern.css, MediaWiki:Monobook.css, and MediaWiki:Timeless.css for now.