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**A binary tree** is a data structure in which **each node can have at most two children**:

- a **left child**
- a **right child**

## Structure

```javascript
        A
       / \
      B   C
     / \
    D   E
```

Here:

- `A` is the root,
- `B` and `C` are children of `A`,
- `B` has two children (`D` and `E`),
- `C` is a leaf (no children).

## Features

- Each node has up to 2 edges (unlike a general tree, where it can have more).
- Simplifies the implementation of search, sorting, and traversal.

## Main types

1. **Complete** - every level is filled except possibly the last, and the elements in it are arranged left to right.
2. **Perfect** - every level is fully filled.
3. **Balanced** - the height of the left and right subtrees differs by no more than 1.
4. **Binary search tree (BST)** - the left subtree contains elements smaller than the parent, the right subtree contains larger ones.

## Summary

**A binary tree** is a hierarchical structure in which each node is connected to at most two children, which makes it the basis for many search, sorting, and data-storage algorithms.

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