One of the important concepts Spring Boot brings in is embedded servers.
Let's first understand the difference between traditional Java web application deployment and this new concept called embedded server.
Traditionally, with Java web applications, we build Web Application Archive (WAR) or Enterprise Application Archive (EAR) and deploy them into servers. Before we can deploy a WAR on the server, we need a web server or an application server installed on the server. The application server would be on top of the Java instance installed on the server. So, we need Java and an application (or web server) installed on the machine before we can deploy our application. The following figure shows an example installation in Linux: