The Internet of Things (IoT) is an ever growing set of connected devices and sensors that are connected through the internet. This can include sensors in cows to your toaster at home. Its purpose is to allow you to collect data and to control devices and systems.
In the home a connected security system allows you to view and control the system from any internet connected device including smart phones, tablet and PCs. A connected refrigerator allows you to add items to a grocery list as you use them, which can be accessed from your phone at the store. It would also allow you to monitor any activity (somebody sneaking ice-cream) remotely.
A connected automobile can be started remotely and activate the air-conditioned or heater insuring a comfortable environment when you get ready to drive. It also allows you to keep track of all maintenance and will notify you when maintenance is needed. On the security side you can lock or unlock your car remotely and track the vehicle when in use.
On the industrial side of IoT connected devices allows operators and managers to monitor and control processes remotely in real time. Reducing costs and waste. It also allows the collection of real time data that can be analyzed to improve the efficiency of operations. The data can include location of items, amounts, run times, etc. Basically if it can be measured the data can be shared with remote devices.
For more information (caution; links access external sites):
In industry: https://www.i-scoop.eu/internet-of-things-guide/industrial-internet-things-iiot-saving-costs-innovation/
In home: https://aws.amazon.com/iot/solutions/connected-home/