What is a jar file

Answer 1

The name is an acronym for Java ARchive. It is a bunch of files -- compiled .class files, text files, images, etc. -- packaged together to run as a single program. On the command line you can run a jar as follows:
java -jar MyProg.jar

Answer 2

A Jar file is a piece of compiled Java code. It's like java's version of an EXE.

Answer 3

Java ARchive format is a package format similar to zip files used to collect associated classes, resources, etc. into one package.