Kinktionary
More like guidelines and a lot less like definitions.
Stag
A typically masculine identifying person who engages in sexual relations with another person or persons, together with their partner, who is referred to as a Vixen.
Part of the enjoyment for a Stag is arranging, thinking of, watching, or hearing about their partner's sexual relationships with others. A stag enjoys their Vixen being desired and sexually enjoying themselves with another person.
Unlike in cuckolding dynamics, there is no humiliation aspect in a Stag and Vixen dynamic. Stags may watch and/or participate as their Vixen engages in sexual relations with others. In some situations, the Stag may not watch or participate at all, but instead, hear about the sexual encounter narrated by the Vixen later, as long as the encounter is communicated well between all individuals participating.
Stags will often reclaim their Vixen after the sexual encounter with others. Reclaiming allows the Stag and Vixen to reconnect as a couple and enjoy the heightened senses that come with the experience of the loyalty and unselfish devotion they have for each other.