You can divide Hearthstone cards by mechanics, by class, by type, by set(basic, expert etc...), by rarity etc... But I couldn't find what is an Elite card? For example Leeroy Jenkins is an elite card.
Can somebody explain?
jw013 is correct. An elite card is one that you can only have one copy of in a deck. As the game currently stands, all elite cards are legendary rarity, and all legendary rarity cards are elite, however in a future update it is possible they may add an elite card that is non-legendary, or a legendary card that can have two copies and is thus not elite, since the elite label is a separate piece of code from the legendary rarity label.