Combinatorial design theory is the part of
combinatorial mathematics that deals with the existence, construction and properties of
systems of finite sets whose arrangements satisfy generalized concepts of
balance and/or
symmetry. These concepts are not made precise so that a wide range of objects can be thought of as being under the same umbrella. At times this might involve the numerical sizes of set intersections as in
block designs, while at other times it could involve the spatial arrangement of entries in an array as in
Sudoku grids.