JavaScript

JavaScript is a prototype-based scripting language with a syntax loosely based on C.

Despite the name, JavaScript is only distantly related to the Java programming language, the main similarity being their common debt to the C syntax.

One major use of web-based JavaScript is to write functions that are embedded in or included from HTML pages and interact with the Document Object Model (DOM) of the page to perform tasks not possible in HTML alone. (source)

LiveJournal uses a lot of JavaScript it many of its pages to provide functionality for the user.