A word, or rather an onomatopoeia first used to title and describe a piece of homosexual pornographic artwork featuring two dragons, whom originated from the animated(anime) series 'Legendz". Since then, it has become somewhat similar to 'Yiff', and could be used to express feelings of approval. Although this is usually confined to the internet.
Person A: Hey, do you like this skin I made to replace the M14 in CS:S?
Person B: Rrerr