Missionary dating is the act of a person of one religious faith, commonly Christianity, dating a person with differing beliefs for the purpose of changing that person's beliefs or religion.
Interfaith dating and interfaith marriage may—or may not—be undertaken in the expectation of converting one's partner, though it is not uncommon for romantic partners to seek to persuade one another to change when there are areas of disunity.
References
Missionary dating Wikipedia(Text) CC BY-SA