The Hook Pattern is a design concept commonly used in programming, particularly in event-driven architectures and frameworks. It allows developers to define placeholders or hooks where custom behaviour can be inserted without altering the underlying structure. Here are its main characteristics:

1. Extensibility: Hooks enable customization of functionality without modifying core logic. Developers can add, modify, or override behaviour, making systems more flexible.

2. Separation of Concerns: Core functionality and user-defined behaviours are kept separate, improving the code's maintainability and readability.

3. Event-driven Nature: Hooks often respond to specific events or stages in a process, making them ideal for implementing event-driven architectures.

4. Non-intrusive: They allow external code to hook into predefined execution points, reducing the need for direct code modification.

5. Reusability: Hooks can be reused across different modules or projects, promoting consistency.

6. Defined Order of Execution: Hooks typically execute in a specific sequence, ensuring predictable outcomes.

7. Decoupling: By defining a standard interface for hooks, systems become decoupled, allowing independent development of modules.

The Hook Pattern is widely used in frameworks like React (e.g., React Hooks), WordPress (action and filter hooks), and middleware systems, enabling developers to build modular, adaptable, and scalable applications.