Sudoku Glossary

This is a list of the terms I'm going to use throughout my Sudoku page. Each one has a specific meaning, so even though certain words may be synonyms in standard English it is possible that they have slightly different meanings when I apply them to Sudoku puzzles. These are arranged in alphabetical order; if you don't know what a term in a definition means, it may be in this glossary as well.

An area is any specified set of cells. It often has a specific constraint.
A box is a region in the shape of an x × y array of cells, where x is the width of the array and y is the height of the array.
A cell is a small square. It can be filled with one (or sometimes more) number, value, or letter. A standard Sudoku puzzle has 9 × 9 = 81 cells.
A clue is a value that a cell is known to have at the commencement of the puzzle.
A column is a vertical, linear region.
A constraint is a rule which the solved Sudoku must obey.
A diagonal is a linear region that is neither vertical nor horizontal.
Disjoint Region
A disjoint region is a region in which traveling along adjacent cells in the region cannot reach all cells from a given starting point.
The grid is the highest-level unit of Sudoku. A grid is an n × n array of cells. The goal of Sudoku is to place a value in every cell of a grid such that all constaints are obeyed.
A region is a set of cells such that the set of the contents of the included cells is equal to a certain, predefined set (order is not important). For a standard Sudoku puzzle, every region must contain the set {1, 2, 3, 4, 5, 6, 7, 8, 9}.
A row is a horizontal, linear region.
A subgrid is a term for one grid out of a puzzle with many grids (for example, a Samurai Sudoku).
Sum Area
A sum area is an area which is constrained to have a certain sum. It is generally accepted that cells within such an area may not ever have the same value.