MMS stands for Multimedia Messaging Service, which is an evolution of the Short Message Service (SMS). MMS adds images, audio clips and ultimately, video clips. These advanced contents can be in different media formats shown below.

Text
Text can be accompanied by images, graphics, sound and video clips.

Graphics
Support for animated colored images, tables, charts, diagrams and layouts.

Audio
Support for music and speech.

Images
Sending images and snapshots from an attached or built in digital camera including ability to edit images and add text.

Video
The ability to send a simple 10-15 sec. clip from handsets with Video recorder (e.g. Nokia 7650 & 3650).

(via Sun Cellular)