In crystallography, a Wyckoff position is a point belonging to a set of points for which site symmetry groups are conjugate subgroups of the space group. Crystallography tables give the Wyckoff positions for different space groups.
Wyckoff positions are used in calculations of crystal properties. There are two types of positions: general and special.
The Wyckoff positions are named after Ralph Walter Graystone Wyckoff, an American X-ray crystallographer who authored several books in the field. His 1922 book, The Analytical Expression of the Results of the Theory of Space Groups, contained tables with the positional coordinates, both general and special, permitted by the symmetry elements. This book was the forerunner of International Tables for X-ray Crystallography, which first appeared in 1935.