JavaScript is a scripting language used to make web pages interactive. It allows embedding scripts directly in HTML and manipulating elements on a web page like changing colors or writing text. JavaScript is object-oriented and uses objects that have attributes and methods. The DOM represents the document as objects that can be manipulated. JavaScript is commonly used to enhance web interfaces through effects like mouseovers and menus. It is also a key part of AJAX which allows asynchronous updating of parts of a web page. JavaScript can collect user input through HTML forms and call functions that process the input. Control structures like if/else statements allow conditionally executing code.