Define a 2D array.

A 2D array, also known as a two‑dimensional array or matrix, is a data structure that stores elements in a grid of rows and columns. It can be visualized as a table where each element is accessed by two indices: the row index and the column index. In most programming languages a 2D array is implemented as an array of arrays. For example, in JavaScript:

const matrix = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
];

Here matrix[0] is the first row, and matrix[0][1] is the element in the first row, second column. 2D arrays are used for matrices, grids, game boards, image pixel data, and any scenario that naturally fits a tabular representation.