Tetrad ('group of 4') or tetrade may refer to: *

Tetrad (area) A tetrad is an area 2 km x 2 km square. The term refers to any of the 25 such squares which make up a standard hectad. Tetrads are sometimes used by biologists for reporting the distribution of species to maintain a degree of confidentia ...

, an area 2 km x 2 km square *

Tetrad (astronomy) In astronomy, a tetrad is a set of four total lunar eclipse A lunar eclipse occurs when the Moon moves into the Earth's shadow. Such alignment occurs during an eclipse season, approximately every six months, during the full moon phase, when ...

, four total lunar eclipses within two years * Tetrad (chromosomal formation) *

Tetrad (general relativity) A frame field in general relativity (also called a tetrad or vierbein) is a set of four pointwise-orthonormal vector fields, one timelike and three spacelike, defined on a Lorentzian manifold that is physically interpreted as a model of spaceti ...

, or frame field **

Tetrad formalism The tetrad formalism is an approach to general relativity that generalizes the choice of basis for the tangent bundle from a coordinate basis to the less restrictive choice of a local basis, i.e. a locally defined set of four linearly independent ...

, an approach to general relativity * Tetrad (geometry puzzle), a set of four simply connected disjoint planar regions in the plane * Tetrad (meiosis), the four cells produced by meiotic cell division *

Tetrad (music) A tetrad is a set of four notes in music theory. When these four notes form a tertian chord they are more specifically called a ''seventh chord'', after the diatonic interval from the root of the chord to its fourth note (in root position close ...

, a set of four notes ** Tetrad (chord), a series of four notes * Tetrad (symbol), or tetractys, a triangular figure of ten points arranged in four rows, and mystical symbol * Medical tetrad, a group of four signs or symptoms which characterise a specific medical condition *

Nibble In computing, a nibble (occasionally nybble, nyble, or nybl to match the spelling of byte) is a four-bit aggregation, or half an octet. It is also known as half-byte or tetrade. In a networking or telecommunication context, the nibble is ofte ...

, or tetrade, a 4-bit group * a

tuple In mathematics, a tuple is a finite ordered list (sequence) of elements. An -tuple is a sequence (or ordered list) of elements, where is a non-negative integer. There is only one 0-tuple, referred to as ''the empty tuple''. An -tuple is defi ...

of length 4 * Tetrad Islands, in the Antarctic

See also