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Refine the answer for “What is a provider (Provider)?”. Your changes go to moderation before they’re published.

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**Provider** is an instruction for Angular on **how to create or where to get a dependency** when it is requested through DI.

In simple terms:
a provider is a **rule** that tells the injector:

> "If someone asks for this service, give them this object."

---

### Example:

```ts
import { Injectable } from '@angular/core';

@Injectable({ providedIn: 'root' })
export class UserService {}
```

Here `providedIn: 'root'` is the **provider**.
It tells Angular: *create a single instance* of `UserService` *in the root injector.*

---

### A provider can also be set manually:

```ts
providers: [
  { provide: UserService, useClass: UserService }
]
```

or, for example:

```ts
providers: [
  { provide: 'API_URL', useValue: 'https://api.example.com' }
]
```

---

### What a provider does:

- specifies **which token** (key) to use (`UserService`, `'API_URL'`, and so on);
- explains **what to return** (`useClass`, `useValue`, `useExisting`, `useFactory`);
- states **where to register it**, in a module, a component, or at the application level.

---

**Summary:**
A provider is a way to tell Angular *exactly how to create or supply a dependency* when it is needed.

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