Mixed marriage
A mixed marriage was a marriage between members of two different species.
In 2404, The Doctor expressed his surprise that Tom Paris would ask whether Lana, the EMH's wife, was a hologram or Human, as he thought making such distinctions would be considered pointless. Paris then clarified that he was glad, being in a mixed marriage himself with B'Elanna Torres (Klingon and Human, in his case). (VOY: "Endgame")