A jar file contains one or more other files. The jar file format is similar to the .zip file format. It is usually used to contain multiple Java class files, image files, and other information needed to bundle a Java application.
A JAR (Java ARchive) file is a file that contains the class, image, and sound files for a Java applet gathered into a single file and compressed for faster downloading to your Web browser. An applet that comes as part of a Web page that you may happen to request may include several files, each of which would have to be downloaded along with the Web page. By putting them in a single file and compressing that file, download time is saved.
Java archive file. A compressed file format consisting of a collection of one or more packages used for Java applications. It includes all the resources necessary to install and run a Java program in a single compressed file.
JAR (Java archive) files are containers for compiled Java source files. They can be associated with an archive (such as, ZIP, JAR) as a source attachment. The children of JAR files are packages. JAR files can be either compressed or uncompressed.
A Java archive. These files typically contain everything needed to execute a Java application or a Java applet. They may also be used to package language-independent information such as data files or images.