Let understand with examples, you are trying to send and receive messages between parts of your app — like one part says, "Hey, a new order came in!" and another part listens for that and does something (like sending an email).

What is a Message Bus?

A message bus is like a middleman that helps parts of your app talk to each other without knowing about each other directly. It's like a delivery service: you drop off a message, and it makes sure the right person gets it.

What is MassTransit?

MassTransit is a tool (or framework) that helps you use a message bus more easily in your .NET apps. It gives you a friendly, consistent way to send and receive messages.

But MassTransit doesn’t deliver messages itself — it uses real delivery services behind the scenes.

What’s the Messaging Library?

This is the actual delivery service — like:

-RabbitMQ

-Azure Service Bus

-Amazon SQS

MassTransit connects to one of these behind the scenes and handles the setup, sending, and receiving for you.

So yes — you're right:

MassTransit is a message bus framework that works on top of real messaging systems (like RabbitMQ or Azure Service Bus). It lets you switch between those systems easily without changing much of your code.