Recently the concept of the semantic web has been coming up in conversations - and many people I talk to don't seem to have a grip on exactly what it is.
A "semantic"(or meaning) web is one in which machines "understand" data. Data about data if you like.
Ostensibly, from a business perspective, the semantic web is about data - but it will likely be much more than this as the idea matures. In time, by using a common language (RDF), a technical ecology will evolve where systems and devices of all kinds can share data and come to understand each other more completely. Many people are talking about the semantic web as the world growing a central nervous system.
As a drugs company. I might want to find out why a particular group of people in an area are more susceptible to diabetes.
At the moment, due to the limitations on the amount and type of data I could practically look at, I might confine myself to the obvious - I might look at smoking rates, or lifestyle data.
In a semantic web world - I would instantly be able to pull in a much wider variety of data from different sources - allowing me to see non linear correlations between the disease and factors I could never have assessed before. Perhaps a DTI data set could tell me how many lorries with toxic waste travel on the nearby roads? Is diabetes related to the amount of dog poo in the local park? Perhaps data on the weather could tell me whether there was any link to above average rainfall?
At a practical level then, the semantic web is about the format of data. The establishing of a common language and systems to enable people to combine information, cut it how they want, and make it more useful for themselves in the real world.