endogamy
practice of marrying within a specific ethnic group, class, or social group
homogamy
marriage between individuals who are, in some culturally important way, similar to each other
avunculate marriage
marriage between an uncle and a niece or between an aunt and a nephew
sibling marriage
marriage between a brother and a sister, or between two brothers, or between two sisters
dynastic marriage
practice of members of ruling dynasties marrying into other reigning families