What is a jnlp file and how do I open a jnlp file?

A .JNLP is a file created in the Java Network Launching Protocol format, used to launch and manage Java programs over a network or on the Web. The file can be double-clicked to run the program if the Java Runtime Environment (JRE) is installed. The JNLP protocol, defined with an XML schema, indicates how to launch Java Web Start applications. A .JNLP is comprised of a set of rules defining how exactly to implement the launching mechanism. A .JNLP file includes information such as the coordinates of the jar package file and the name of the main class for the application, in addition to any other parameters for the software. A properly configured web browser passes JNLP files to a Java Runtime Environment (JRE) which then downloads the application onto the user's machine and commence executing it. JNLP mirrors this process; in the same way that a Web browser renders a webpage, a JNLP client "renders" a Java app. After the user clicks on a weblink, the browser submits an URL to a webserver, which replies with a JNLP file (instead of a HTML file) for the application. The JNLP client separates this file, requests the resources specified (jar files), waits for the retrieval of all necessary resources, and then launches the application. The JNLP file can list resources as "lazy", which informs the JNLP client that the application does not need those resources to start, but can retrieve them later on when/if the application requests them.