Tetrad

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


 * Tetrad (area), an area 2 km x 2 km square
 * Tetrad (astronomy), four total lunar eclipses within two years
 * Tetrad (chromosomal formation)
 * Tetrad (general relativity), or frame field
 * Tetrad formalism, 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 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, or tetrade, a 4-bit group
 * a tuple of length 4
 * Tetrad Islands, in the Antarctic