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.
See Also: 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.
See Also: HTML, Java

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
See Also: Applet , Java

JPEG
(Joint Photographic Experts Group) -- JPEG is most commonly mentioned as a format for image files. JPEG format is preferred to the GIF format for photographic images as opposed to line art or simple logo art.
See Also: GIF