What is XML-RPC protocol ?
XML-RPC is a simple, portable way to make remote procedure calls over HTTP. It can be used with Perl, Java, Python, C, C++, PHP and many other programming languages. Implementations are available for Unix, Windows and the Macintosh.
In order to update your WordPress website from your mobile phone or another remote location, you need to enable XML-RPC (XML Remote Procedure Call). See http://www.sitepoint.com/xml-rpc-for-wordpress-developers/ for excellent article.