"Knowledge worker, a term coined by Peter Drucker in 1959, is one who works primarily with information or one who develops and uses knowledge in the workplace"
Here are some characteristics of a knowledge worker that I would like to add to that definition:
1. Your work and spare time is not defined by office hours
Your brain is not turned on at 8 .00 AM and turned off at 17.00 PM. If it was, you would not be able to do your job as a knowledge worker. A problem solving process continues in the back of your mind until it is completed and the problem is solved (or you have to finally leave it unsolved). Cognitive processes in your brain are constantly receiving input, interpreting it into information that you transform to knowledge when you apply it. You constantly prepare yourself and progress towards your goals by digesting information and planning your next actions. When you step out of the shower you might know exactly how things relate or how to attack a problem that you are working with. You write it down, let it go and continue with breakfast.
2. Your results and contributions are more important than face time at the office
If you have no tasks or meetings immediately at hand during office hours, you take a break to home to be with your kids, enjoy a walk in the park, meet with a friend or work out at the gym. You take the time off to let things fall into place as your cognitive processes are still being executed in the back of your mind. You don't just sit off your time in front of the computer when your mind is full enough of other things to digest. You know that you sometimes need to change environment to avoid cognitive deadlock. You know that it is your results and contributions that matter to your employer or customer and you have the mindset to deliver what you are expected to deliver. You have confidence enough to prioritize results before face time.
3. Your availability is more important your being physically present during office hours
You sometimes meet with colleagues and customers outside of the office in a more relaxed and creative environment. And you check things with colleagues during any time of the day. You know that a customer or colleague might call you, chat with you or send you an e-mail after office hours and you are mentally prepared to react when needed. It doesn't bother you since things are often not urgent after office hours and you probably can find a time slot sooner or later to react on them, and it usually has to do with simple status checking that does not require a lot of your time. And you utilize the kind of communication channel that is most convenient and suited for the situation you are currently in. Then you let it go from your mind and continue with whatever you were doing.