Twilio is a communication platform that allows developers to power real-time communications and messaging in web, mobile, desktop, and embedded applications. In this tutorial, Diane Phan shows how to send scheduled SMS with Twilio using Java. The process involves creating a Twilio account, purchasing a phone number, configuring a Messaging Service, downloading the Twilio Java helper library, adding dependencies to the project, setting environment variables, and scheduling an SMS using the `Message.creator()` function. The tutorial provides step-by-step instructions and code examples to help developers send scheduled SMS notifications in Java.