The mobile Web is simply the term we use when we're talking about browsing the Web - yes, the same Web you can surf on your desktop computers or laptops - on our cellphones or mobile devices. However, the similarities end there.
For instance, while you can access many of the same sites on the mobile Web that you visit on your computer, the sites will most likely not look the same. Why? Mostly because of space constrictions. After all, the smaller screens that mobile devices require don't lend themselves very well to the same graphics that we've become accustomed to otherwise. In addition, navigation is slow and tedious on most mobile devices, since the options pretty much end at up and down scrolling (no mouse).
Last, but definitely not least, accessing sites on the mobile Web can be extremely slow, which makes for a very frustrating Web experience - and costly, too. While surfing the Web on your computer usually comes out as a flat monthly rate to your local Internet service provider, the cost of accessing the mobile Web depends on your cellphone service plan, which can be surprisingly steep.
Even with these restrictions, more people than ever before access the Web on their cellphones, reading the news, contributing to social networking sites, blogging, and searching the Web. The mobile Web has a long ways to go, but the more that people use it and up the demand for better accessibility, the more improvements we should expect to see.