Mobile web development is web development focused on developing a site to be viewed on mobile browsers and working through the relevant use cases and the design/functional/technological things that come with those use cases.
The mobile web is very much a context-, content-, and component-specific environment. Or put another way, access to web content on a mobile device is largely influenced by surrounding conditions, informational relevance to the task at hand, and the feature capabilities of the device being used. Unlike the desktop web experience, where screen space is liberal, web access is fast and reliable, and data input is facilitated by keyboard and mouse, the mobile web experience is often a small screen, intermittent, one-handed experience. Invariably, this often leads to leaner content and a reduced feature set in comparison to desktop web content, but it also leads to opportunities unavailable in the desktop web environment: location-specific data, on-the-go messaging, and of course voice communication to name a few.