a sphere of activity with a standard to be maintained over time
Essentially, categories of your life where you have responsibilities. The "standard" part is important, and is only defined by you: if you feel as though you aren't keeping up your standards, make a project to get back on track. "Responsibility" is also important: if it's only an interest, it's a resource.
Because of this, areas of responsibility should be specific: not "Personal", because how do you judge if you're living up to your standards of "Personal"? Instead, "Finances", "Spouse", etc.
a project without a corresponding goal is known as a “hobby" . . . . if you have a goal without a corresponding project, that’s called a “dream".
Remember: separate actionable items from non actionable. This will allow you to work on what matters.