Decisions about what kinds of hardware and software to purchase, how to install and tune it, and what to do when it breaks are examples that most readers can relate to.
Some people call it instinct or gut feel - it's all the same thing.
It's the sum total of our ability to relate what we learn from different sources filtered through trial and error. A classic example of the need for clear professional judgment often occurs when a system made up of components from multiple vendors fails. As the user, you may not have a clear understanding of how the pieces interact. There may be no one on your team who does. And then suddenly, there you are in a meeting with people from several suppliers who can't even agree on what the problem is, much less a viable solution.