From Wikipedia on 10/13/12
A series of events to produce a result, especially as contrasted to product.
My Own Writing
There’s a difference between a system and a process. A system is a collection of related elements. A process is the movement of information, matter, or energy through a system.
You can think of a process as equivalent to a function in a computer program. It has inputs, outputs and transformations. Certain things are read and certain things are written. It may call or be called by other processes. For example, in sorting your mail, the box of unsorted mail is read and the notebooks that the sorted pages of mail go into are written.
A process is always a pattern. A pattern is something that retains its form, even though the individual elements that make it up may change. A river is a pattern. As Heraclitus said, you can never step into the same river twice. We see it as a consistent object, even though the elements that make it up are constantly changing, as they sweep through it. Human beings are like rivers in that way. The molecules that make up our bodies are supposedly changed out every seven years, but the pattern remains. Social processes are patterns too, because even though the individual people may change, the things they go through in their lives are similar. There are similarities. Any feedback loop process probably exhibits similarities to any other. Even though the names change in news stories, the pattern remains the same.