|"Cuz we all know penguins have sexy boobs"|
BREEDABLES - a fun way to throw away lots of money that would otherwise be wasted on rent or mortgage.
ESCORTS - will pretend they actually care for you if you throw enough lindens at them. Most likely male in RL. and if female, is probably ugly.
FURRIES - people whose pets hide when they coo "i wuf u".
LINDENS - pretend money used to pay for pretend mansions, where you can engage in pretend sex and raise pretend families. The conversion rate to US dollar depends on the waxing and waning of the full moon, and the general mood and disposition of certain Linden Lab employees. Rumor has it that Oat Bran in the morning results in a strengthening of the linden against the dollar due to higher flow rates.
RL - that thing that everyone in SL desperately wants to avoid.