The Internet of Things (IoT) is the interconnection of heterogeneous objects through the Internet. This concept was created by Kevin Ashton.
Then, in this community, we talk and solve questions about how to interconnect different objects through the Internet.
These objects are heterogeneous because they can be microcontrollers like an Arduino, a microcomputer like a Raspberry Pi, different sensors, actuators, smartphones, cars, and so on. Anything that you have in your mind. Besides, these objects are ubiquitous because they can be in anywhere: in your home, in movement in the highway, in the sea, crossing the sky, etc. The only thing that these objects need is a connection to the Internet to have the possibility to send messages to other objects. Furthermore, these objects can be intelligent, also called Smart Objects, or not, like sensors and actuators. You can read more about the Smart Objects, Sensors, and Actuators here.
Then, in this community, you can find and ask about how to connect these objects, the problems that you have installing or configuring these objects, or other doubts that you could have about it.
Here you can read a very good survey that talks about the IoT is.