the practice of marrying outside one's own group.

marriage to a person belonging to a tribe or group other than your own as required by custom or law

outmarriage, marriage to an individual outside of a defined social group, category, or range.

marriage outside a particular group with which one is identified.

Marriage to a person from outside one's own group (kin or community).

Rules (not necessarily codified) requiring marriage outside a group, e.g. a kinship group or lineage. Exogamy creates ties between groups. (See endogamy)

Marriage outside the group.

The custom of marrying outside the tribe, family, clan or other social unit.