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**Currying** is the process of transforming a function that takes several arguments into a sequence of functions, each of which takes **only one argument**.

---

### Example:

A regular function:

```javascript
function sum(a, b) {
  return a + b;
}

sum(2, 3); // 5
```

After currying:

```javascript
function curriedSum(a) {
  return function (b) {
    return a + b;
  };
}

curriedSum(2)(3); // 5
```

---

### How it works:

- `curriedSum(2)` returns a new function that "remembers" the value `a = 2`.
- That function then waits for the second argument `b`.
- When we call it with `3`, it returns the result `2 + 3`.

---

### Why currying is needed:

1. **Reusing partially applied functions**

```javascript
  const add10 = curriedSum(10);
  add10(5); // 15
  add10(7); // 17
  ```
2. **Simplifies function composition** - useful in functional programming.
3. **Improves code readability and flexibility**, especially in libraries like Lodash or Ramda.

---

### In short:

> Currying turns the function `f(a, b, c)` into `f(a)(b)(c)`,
> so it can be called in parts and partial calls can be reused.

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