Message Bus:

A message bus is a conceptual abstraction that allows components or services to communicate with each other asynchronously by sending and receiving messages. It decouples the sender and receiver, promoting loose coupling and scalability.

In practice, a message bus is often implemented using a messaging library or broker, such as RabbitMQ, Azure Service Bus, or Kafka.

You can think of a message bus as a pattern or interface that hides the implementation details of the underlying transport mechanism.

MassTransit is a .NET framework for building distributed applications using messaging. It implements the message bus pattern and provides:

• A consistent abstraction over different message transports (RabbitMQ, Azure Service Bus, Amazon SQS, etc.)

• Features like consumers, sagas, middleware, routing, serialization, and retries

• Developer-friendly APIs to handle complex messaging workflows

• A message bus is an abstract concept or interface.

• MassTransit is a concrete implementation of a message bus pattern.

• MassTransit allows you to plug in different underlying messaging libraries (such as RabbitMQ or Azure Service Bus) without modifying your business logic.

So yes — MassTransit is a message bus implementation that can work with multiple messaging libraries under the hood.