A converso was a Jew who converted to Catholicism in Spain or Portugal in the Iberian Peninsula, particularly during the 14th and 15th centuries, or one of his or her descendants forced to convert to Christianity during the Middle Ages.
The Catholic monarchs Ferdinand and Isabella expelled those remaining openly practising Jews by the Alhambra decree of 1492, following the Christian Reconquista (reconquest) of Spain. However, even a significant proportion of these remaining practising Jews chose to join the already large converso community rather than face exile.
Those who continued to practice Judaism in secrecy were called Marrnos. The term specifically refers to the charge of crypto-Judaism. Crypto-Judaism is the secret adherence to Judaism while publicly professing to be of another faith. The phenomenon is especially associated with renaissance Spain, following the Massacre of 1391 and the expulsion of the Jews in 1492.