To understand Selenium Grid, we need to understand the concept of hub and nodes. There is only one hub, but there can be multiple nodes.

The hub is the central machine which sends commands to the respective nodes based on parameters.

The node is the machine where our test will be executed.

The following diagram shows the architecture of Selenium Grid. This diagram shows that we have one hub and there are four nodes: one for Mac, one for Windows, one for Linux, and one for Android:

Let's move on to the basic setup of Selenium Grid.