Any idea for a new and non-obvious useful article of manufacture, process, machine or composition of matter, or use thereof, or for a new and non-obvious improvement on old articles, processes, machines or compositions.

There are two stages to an invention: Conception, that is, coming up with the idea; and Reduction to Practice, that is, taking the initial idea and bringing it to a level by which anyone could use it. Actual Reduction to Practice is typically creation of the article or carrying out the process. Constructive Reduction to Practice is filing a patent application having adequate description in it to allow anyone reading it to be able to make the article or practice the process.