Web animation is any kind of animation made for a website. It employs an extended format which can be generally visualized through a web navigator. These web animations are created with different technologies: Shockwave Flash, animated GIFs, plug-ins, dynamic HTML, among others.

How is Web Animation Made?

Web animation is made by expert programmers. To achieve the illusion of movement, an image is displayed on the computer screen and repeatedly replaced by an image similar to the previous one at a rate of 24 to 30 frames per second.

Animated GIFs

In web animation, a bitmap file describes the color of each image's pixel. These bitmap files are used in websites and texts. The animated GIFs, which are encountered throughout the Web, are a series of bitmap files shown in sequence.

Dynamic HTML

Dynamic HTML uses a complex script language such as JavaScript to access the document object model on the Internet browser. This document object model controls the entire status of the browser. With this, movement is added to web sites; although it is a static movement, since the object moves as in a slide.

Plug-Ins

Plug-ins appeared in the nineties. They are small pieces of software which allow users to reproduce movie or animation files. They are very practical since most of the plug-ins are downloaded from the same web pages where they appear.

Shockwave and Flash

Flash is the standard format for rich animation on the web, and Shockwave allows the programmer to create more complex animations. With Shockwave files, the viewer can interact with the animation, like in a game. Even more, Shockwave adapts the animated file to the viewer's browser controls.

Source:

How Stuff Works: How Web Animation Works