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A **two-dimensional array** (or *array of arrays*) is a data structure
in which **each element is itself an array**.

Put simply, it is a table:
rows and columns, like in Excel or a matrix.

---

## Example of a two-dimensional array:

```javascript
const matrix = [
  [1, 2, 3],   // ← row 0
  [4, 5, 6],   // ← row 1
  [7, 8, 9]    // ← row 2
];
```

Here:

- `matrix[0]` → `[1, 2, 3]` (the first row)
- `matrix[1][2]` → `6` (an element from the second row, third column)

---

## Visually:

```javascript
[
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
]
```

|  | 0 | 1 | 2 |
|---|---|---|---|
| **0** | 1 | 2 | 3 |
| **1** | 4 | 5 | 6 |
| **2** | 7 | 8 | 9 |

---

## How to access elements

```javascript
console.log(matrix[0][0]); // 1
console.log(matrix[2][1]); // 8
```

The first index is the **row**,
the second is the **column**.

---

## How to iterate over all elements

### With nested loops:

```javascript
for (let i = 0; i < matrix.length; i++) {
  for (let j = 0; j < matrix[i].length; j++) {
    console.log(matrix[i][j]);
  }
}
```

- `i` is the row number,
- `j` is the column number.

---

## Example use case:

Two-dimensional arrays are often used for:

- storing tables and matrices of numbers;
- representing game boards (for example, chess, tic-tac-toe);
- storing coordinates (x, y);
- working with images, pixels, grids, and so on.

---

## Creating an empty two-dimensional matrix:

```javascript
const rows = 3;
const cols = 4;
const matrix = Array.from({ length: rows }, () => Array(cols).fill(0));

console.log(matrix);
/*
[
  [0, 0, 0, 0],
  [0, 0, 0, 0],
  [0, 0, 0, 0]
]
*/
```

---

## In short:

| Term | Meaning |
|---|---|
| Two-dimensional array | An array where each element is an array |
| Indexing | `[row][column]` |
| Example | `matrix[1][2] → 6` |
| Often used for | Tables, grids, coordinates, matrices |

---

> **Summary:**
> A **two-dimensional array** is a "table in code":
> an array made up of other arrays.
> It lets you conveniently store data as **rows and columns**.

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