Webhooks are one way to send automated messages or information to other apps.
Examples; It's how PayPal tells your accounting app when your clients pay you, how Twilio routes phone calls to your number, and how WooCommerce can notify you about new orders in Slack.
They're a simple way your online accounts can "speak" to each other and get notified automatically when something new happens. In many cases, you'll need to know how to use webhooks if you want to push data from one app to another automatically.
As Always, Happy Ordering.