Introduction to the mobile web

For all who is fairly to mobile web development and wants a first introduction, I can recommend the Opera documentation pages and more specific these documents:

Mobile 1: Introduction to the mobile web

Mobile markup - XHTML Basic 1.1

The article also states clear that we are not talking about mobile applications like you can find in the Android Market, iphone store, Nokia Ovi, ....
Mobile web sites tend to provide a way of bringing information that is available on the web towards multiple devices, including a mobile device.

The W3C has been pushing the idea of "One Web". "[This] means making, as far as is reasonable, the same information and services available to users irrespective of the device they are using. However, it does not mean that exactly the same information is available in exactly the same representation across all devices. The context of mobile use, device capability variations, bandwidth issues and mobile network capabilities all affect the representation. Furthermore, some services and information are more suitable for and targeted at particular user contexts." Source: the W3C Mobile best practices one web page.