After installing the Selenium Server, it is possible to test local and remote web applications by using any of the browsers installed in the Server. For small teams, a single server might be enough to test all of the team's applications. However, for teams that have to deal with a considerable amount of web applications, Selenium provides an option called Selenium Grid. As of Selenium 2.0, the Server now incorporates the functionality of Selenium Grid.

As you can see in the following diagram, test automation scripts can request to be run on a specific combination of operating systems and browsers. The Selenium Hub distributes those requests to the suitable nodes. Nodes are (physical or virtual) instances of the Selenium Server that allow you to test applications under a wide variety of operating systems (Windows, macOS, Android, and so on) and browsers (Internet Explorer, Chrome, Safari, and so on).

A grid consists of several systems running the server software in a hub and node configuration. We will take a more thorough look at the Selenium Grid in Chapter 9, Using a Selenium Grid.