Definition of arroba:
(n) :
(historical) A traditional Spanish unit of mass, varying by time, location, and substance but generally around 11.5 kilograms.
(n) :
(historical) A traditional Portuguese unit of mass, usually equivalent to 14.7 kilograms.
(n) :
(historical) A traditional Spanish unit of liquid measure, varying by time, location, and substance but generally around 15 liters.