dyad may refer to:
* dyad (biology), a pair of sister chromatids occurring in prophase I of meiosis. Can also be used to describe protein morphology using the definition here: [1].
* dyad (Greek philosophy), Greek philosopher's principle of "twoness" or "otherness"
* dyad (music), a set of two notes or pitches
* dyad (sociology), mostly refers to pairs of individuals such as couples, co-authors, twins, and so on.
* dyad pedagogy, in education.
* dyad, in engineering kinematics, a linkage in a planar mechanism that has two possible assembly modes
* dyad, in Obstetrics refers to the pregnant mother and fetus
* dyadic tensor, in mathematics