Describe each mechanism: Webhook, Callback, Polling (periodic polling).

Webhook is a mechanism where a server automatically sends a notification (usually an HTTP POST) to a pre-defined client URL when a specific event occurs. The client receives data immediately, without the need to poll the server.

Callback is a more general term that refers to a function or URL that is called in response to an event or the completion of an operation. On the web, a callback is often implemented via a webhook or by passing a callback function in code.

Polling (periodic polling) is when a client regularly (for example, every N seconds) sends requests to a server to check if new data or events have appeared. This is less efficient than a webhook because it generates unnecessary traffic and delays in data reception.

Example:

• Webhook: the server immediately notifies the client of a new message.
• Polling: the client asks the server every minute if there are new messages.

Webhooks are more efficient and reactive, polling is easier to implement but less resource-efficient.