A Message Broker is a software component that facilitates communication between different applications or systems by receiving, forwarding, and delivering messages. It acts as an intermediary, transporting messages from one application to another regardless of the type of application or its location.

The Message Broker receives messages from a sending application, temporarily stores them, and then forwards them to the respective receivers. The broker can provide various functions such as message queues, topics, message routing, and transformations to ensure that messages are transmitted efficiently and securely.

Such systems are often used in distributed application landscapes to facilitate interaction and data exchange between different applications, services, or systems by enabling loosely coupled, reliable communication.

A web application is a software application accessible via a web browser and operates over the internet. Unlike traditional software installed on a local computer, a web application runs on a remote server and is accessed through the user's browser.

Web applications can encompass a wide range of functions, from simple interactive pages to complex applications such as social networks, email services, online stores, productivity tools, and more. They often use a combination of different technologies like HTML, CSS, and JavaScript on the client-side (in the user's browser) as well as backend technologies like databases, server-side scripting languages (e.g., Python, PHP, Ruby), and frameworks to support functionality.

Accessing web applications via the browser makes them platform-independent, allowing them to be used from various devices with an internet connection—be it a computer, tablet, or smartphone.