CHARSET, qu'est-ce que l'encodage et comment configurer son serveur?

MySQL

SHOW SESSION VARIABLES like "char%";
SHOW GLOBAL VARIABLES like "char%"; 

// SESSION
character_set_client => utf8
character_set_connection => utf8
character_set_database => latin1
character_set_results => utf8
character_set_server => latin1
character_set_system => utf8
character_sets_dir => /usr/share/mysql/charsets/

// GLOBAL
character_set_client => latin1
character_set_connection => latin1
character_set_database => latin1
character_set_results => latin1
character_set_server => latin1
character_set_system => utf8
character_sets_dir => /usr/share/mysql/charsets/

PHP

define('CHARSET'       , 'utf-8'); // utf-8, iso-8859-15, cp1252...
define('LOCALE'        , 'fr_FR'); // Attention aux diff. systemes (windows / linux)
define('MYSQL_CHARSET' , 'UTF8');  // UTF8, latin1...

@ini_set('default_charset', CHARSET);
setlocale(LC_ALL, LOCALE, 'fr_FR.'.CHARSET, 'fr_FR', 'fra');
header('Content-Type: text/html; charset=' . CHARSET);

$sql = "SET NAMES " . MYSQL_CHARSET;
mysql_query($sql);

HTML

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />