An invention is a new thing that someone has made. The computer was an invention when it was first made. We say when it was "invented". New things that are made or created are called inventions. Cars and plastics are inventions that everyone knows. Inventions are made by inventors...An invention is defined as a device, method or process developed from study and experimentation.
When a invention is created it can be protected by a patent. A patent is a set of exclusive rights granted by a state or national government given to an inventor for a limited period of time in exchange for a public disclosure of an invention.
Sometimes a device is invented before there is a need. For example, the can opener was invented 48 years after cans were introduced, and traffic lights were used before the advent of the motorcar.
Most of the time an invention is created because of a need. For example, before the invention of the thermometer, the brewers of beer used to check the temperature by dipping their thumb into the mixture to find whether the temperature was appropriate for adding yeast. If it was too hot, the yeast would die. This is where we get the phrase ” The Rule of the Thumb”.