User blog comment:Lesanthosxia/My Opinion: Leona's teamplay and my built./@comment-569195-20111024195359/@comment-3358335-20111025202455

Support is defined by the character that keeps other characters alive in team fights. Support - Champ that keeps their team alive by providing buffs to team or debuffs to enemies.
 * Tank - Guy that takes hits and provides CC. By taking the damage meant for others, or preventing damage to others he keeps his team in the fight longer.
 * Ranged AD - Character that does a majority of his damage from auto attacks from afar
 * Melee AD - Character that does a majority of his damage from auto attacks up close and personal.
 * Mage - Provides Magic damage and some sort of hard cc
 * Assassin - Bursty damage Squishey champ with gap closer rather than hard CC (gap closer could be stealth, could be leaps, could be blinks)

It has nothing to do with what lane they take.