JAR
A popular compression format. Also a name of a compression utility.

Java
Java is a network-oriented programming language invented by Sun Microsystems that is specifically designed for writing programs that can be safely downloaded to your computer through the Internet and immediately run without fear of viruses or other harm to your computer or files. Using small Java programs (called "Applets"), Web pages can include functions such as animations, calculators, and other fancy tricks.

We can expect to see a huge variety of features added to the Web using Java, since you can write a Java program to do almost anything a regular computer program can do, and then include that Java program in a Web page.

Java Applet
Most often refers to a small Java program designed to run in a Web browser.

Java Class Files
The file or set of files that contain the code for a Java applet.

JavaScript
JavaScript is a programming language that is mostly used in web pages, usually to add features that make the web page more interactive. When JavaScript is included in an HTML file it relies upon the browser to interpret the JavaScript. When JavaScript is combined with Cascading Style Sheets (CSS), and later versions of HTML (4.0 and later) the result is often called DHTML.

JavaScript was invented by Netscape and was going to be called "LiveScript", but the name was changed to JavaScript to cash in on the popularity of Java. JavaScript and Java are two different programming languages.

Java Servlet
A servlet is an application or a script that is written in Java and executed on a server, as opposed to on a client. It is analogous to CGI, although servlets are more than simply CGI scripts written in Java.

JDBC
Java Database Connectivity. A mechanism allowing Java applets to access different databases.

JDK
Java Development Kit. A software development package from Sun Microsystems that implements the basic set of tools needed to write, test and debug Java applications and applets.

JPEG
Joint Photographic Experts Group. The group which creating the JPEG image format. Also know as the jpg format. The main advantage of JPEG over GIF is its high compression rates.

A photo can be converted to the JPEG format and published on the Internet at small file sizes, thus saving bandwidth and loading times of web pages.

JScript
Microsoft's implementation of ECMAScript standard based on JavaScript. Limited, object-based, interpreted scripting language. Here is the official JScript site. JScript is comparable to VBScript.

JSP
Java Server Pages. Extension of Java Servlet technology for combining Java server-side programs and HTML. JSP pages have an extension .jsp.

JVM
Java Virtual Machine. A set of programs that allow for Java applets to be run on a particular computer system.