(1) (Java ARchive) A file format that contains multiple files and is used to distribute a complete Java application. It contains all the resources required (classes, images, sounds, etc.) to download and run a Java program via a single HTTP request for one file. JAR files use the ZIP format and are the basis for WAR files. See WAR and EAR.

(2) A compression program for backup archiving from ARJ Software, Inc., Norwood, MA (www.arjsoftware.com). JAR is similar to ARJ, but files are not compatible. See ARJ.