In geometry, a hyperrectangle (also called a box, hyperbox, ${\displaystyle k}$-cell or orthotope), is the generalization of a rectangle (a plane figure) and the rectangular cuboid (a solid figure) to higher dimensions. A necessary and sufficient condition is that it is congruent to the Cartesian product of finite intervals. This means that a ${\displaystyle k}$-dimensional rectangular solid has each of its edges equal to one of the closed intervals used in the definition. Every ${\displaystyle k}$-cell is compact.

If all of the edges are equal length, it is a hypercube. A hyperrectangle is a special case of a parallelotope.

For every integer ${\displaystyle i}$ from ${\displaystyle 1}$ to ${\displaystyle k}$, let ${\displaystyle a_{i}}$ and ${\displaystyle b_{i}}$ be real numbers such that ${\displaystyle a_{i}<b_{i}}$. The set of all points ${\displaystyle x=(x_{1},\dots ,x_{k})}$ in ${\displaystyle \mathbb {R} ^{k}}$ whose coordinates satisfy the inequalities ${\displaystyle a_{i}\leq x_{i}\leq b_{i}}$ is a ${\displaystyle k}$-cell.

A ${\displaystyle k}$-cell of dimension ${\displaystyle k\leq 3}$ is especially simple. For example, a 1-cell is simply the interval ${\displaystyle [a,b]}$ with ${\displaystyle a<b}$. A 2-cell is the rectangle formed by the Cartesian product of two closed intervals, and a 3-cell is a rectangular solid.

The sides and edges of a ${\displaystyle k}$-cell need not be equal in (Euclidean) length; although the unit cube (which has boundaries of equal Euclidean length) is a 3-cell, the set of all 3-cells with equal-length edges is a strict subset of the set of all 3-cells.

A four-dimensional orthotope is likely a hypercuboid.

The special case of an n-dimensional orthotope where all edges have equal length is the n-cube or hypercube.

By analogy, the term "hyperrectangle" can refer to Cartesian products of orthogonal intervals of other kinds, such as ranges of keys in database theory or ranges of integers, rather than real numbers.