tríada

Tríada is a term used in Portuguese, Spanish, and other Romance-language contexts to denote a group, set, or system of three related items or people. The concept functions as a general structural idea across disciplines, describing triads in philosophy, theology, sociology, and the natural and social sciences.

In music, a tríada, or triad, is a chord consisting of three distinct notes stacked in thirds, typically a root, a third, and a fifth. Common varieties include major, minor, diminished, and augmented triads. Triads form the building blocks of tonal harmony and are named after their root note (for example, the C major triad consists of C, E, and G).

In social science, a triad refers to a group of three actors in a social network. Triadic relationships can have dynamics different from dyads (two-person groups), including triadic influence and triadic closure, the tendency for two people who share a common acquaintance to become connected themselves.

Historically and culturally, the word also designates organized crime groups known as Triads in Chinese communities, or tríadas in Portuguese-speaking contexts. These organizations are secret societies with initiatory traditions and a presence across Greater China, Southeast Asia, and diaspora communities. In chemistry and related fields, the term triad has been used to describe sets of three related elements or principles, such as Dobereiner’s triads in early attempts to classify the periodic table.