In medieval Spain this usually referred to a coin representing one half of any denomination. 2. A silver 1/2 real struck by Juan I of Aragon (1387-1396). 3. A billon and silver coin of Cataluna. 4. A silver grano struck by Felipe II of Spain, while ruler of Naples and Sicily. 5. A minor coin of medieval Europe, valued at 1/2 dinero. It was called a miaja in Castilla, Aragon, Portugal and called a malla in Cataluna and Valencia. These words continued as slang to refer to coins of little value in centuries to follow.
Source: Numiscadero Spanish to English Glossary (Gary Beals)