Marranos are originally Jews living in Iberia who convert or are forced to convert to Christianity, some of whom may continue to practice Judaism in secret.

The term comes into later use in 1492 with the Castilian Alhambra Decree, reversing protections originally in the Treaty of Granada (1491).The converts are also known as cristianos nuevos (Spanish) or cristãos-novos (Portuguese), meaning "New Christians", or conversos (converted ones).

In Hebrew the terms anusim ("forced ones") and Zera Yisrael ("seed of [the people of] Israel") are sometimes used.