Jetty is a widely used web container (server) written in Java and produced by Eclipse.
Jetty is a widely used web container written in Java. Jetty has a slogan, "Don't deploy your application in Jetty, deploy Jetty in your application."
What this means is that as an alternative to bundling your application as a standard WAR to be deployed in Jetty, Jetty is designed to be a software component that can be instantiated and used in a Java program just like any POJO. Put another way, running Jetty in embedded mode means putting an HTTP module into your application, rather than putting your application into an HTTP server.
You can find extra information for Jetty at Codehaus.