A tertiary partner is a term used within the context of polyamory and ethical non-monogamy (ENM) to describe a romantic or sexual partner who is not one of the primary or secondary partners in a relationship structure.

Typically, in polyamorous dynamics, the relationship hierarchy may be categorized into primary partners (those with the most significant emotional or logistical commitment), secondary partners (those with a substantial but lesser commitment), and tertiary partners, who may have more casual or less frequent connections.

While a tertiary partner may still share intimacy and affection, the nature of the relationship is often characterized by less emotional or logistical entanglement. For instance, a tertiary partner might be someone with whom a person has occasional dates or sexual encounters, without the expectation of long-term commitment or integration into each other’s daily lives.

In contrast to primary or secondary partners, a tertiary partner might not be involved in group activities or decision-making processes regarding the primary relationships, and their role can vary widely based on the agreements and dynamics established within the broader polyamorous network.

In practice, the distinctions among partners are frequently fluid, and individuals may find themselves moving between these categories over time as relationships evolve.