Wikipedia cites various descriptions of it - "the networked interconnection of everyday objects" or a "self-configuring wireless network of sensors whose purpose would be to interconnect all things" - but part of its value as a term (at the moment, anyway) is its vagueness.
People sort of know what it means, or what they'd like it to mean, and it's a broad enough church that all sorts of ideas get swept together and acquire a decent bit of momentum. It's a bit like "Web 2.0"; it'll be aspirational for a moment, then there'll be lots of hype, then there'll be religious wars about what's in and what's not, then lots of piss-taking about all the Internet of Things cliches. But the basic idea is to think about - and try to build something that enables - what happens when all the things in our lives get connected, can talk to each other and know something about their status and their place in the world.
The cliches are probably familiar - the fridge that knows you're low on milk and can update the shopping list in your car, the car that knows it's close to home and can talk to the house and turn the heating on, the kettle that knows you're coming downstairs and turns itself on to get the tea started. Some of these things already exist. Individual products are already getting smarter and are occasionally connecting to other smart things.
It's a bit like the early days of computing: individual machines got cleverer, then started to enhance themselves by interoperating with peripheral input and output devices - just as your smartphone and your brand new car can probably talk to each other in a limited way at the moment. Then computers that were physically near each other got connected up by cables.
Then there was the really big bang when internet protocols allowed machines everywhere to connect easily and quickly to machines everywhere else. And we suddenly got all sorts of unpredictable and unexpected effects.
People invented things to sit on these networks - such as e-mail and the web and spam and viruses - and we suddenly acquired all sorts of new problems and opportunities.
Well, that's what happened when we connected the people and the computers - among the side effects was the complete disruption of our business. Next week, we'll think about what happens when we connect the cereal packets and the vacuum cleaners.