No less than three top ten lists of things everyone should know about philosophy have been published on philosophy blogs in recent days.
The best of the three is at DuckRabbit. This list is entirely about how philosophy works, and not particular philosophical ideas the author thinks you should believe in. I think I agree with everything he says.
The list that started it all is at Philosophy, et cetera. I don't much care for this list on the whole, because I don't think it's really a list of things people should know about philosophy (that is, it isn't about meta-philosophy as the DuckRabbit list is), but instead includes a bunch of philosophical ideas the author thinks you should accept, and I disagree with a lot of these ideas. This gets progressively worse the farther down the list you go.
The third and final list is at Mormon Metaphysics. I like this list too.
I don't have time to write my own top ten list right now (busy writing my archaeology term paper still), but let me just link you to these three, and give you my definition of philosophy: philosophy is the application of logic in the pursuit of truth. Therefore, as Duck says, philosophy is "open to everyone to do, but you aren't doing it simply by saying you are (nor are you not doing it simply because you don't know that you are; on the other hand if you don't know that you're doing it you probably aren't doing it very well)." All sane and rational people do philosophy from time to time, just like all sane and rational people do physics from time to time (when they 'calculate' intuitively where that baseball is going to land, or how much force to apply to open the door without breaking it, or whatever), but that doesn't make them all philosophers or all physicists. Some people devote their lives to such things. You will also notice that my definition is so broad that it makes most academic disciplines sub-fields of philosophy. This is intentional, and the reason it's intentional is that historically they all 'spun off' of philosophy. Today, the people who are in the actual philosophy department are those who try to put everything together from all the fields, or those who work on fields such as metaphysics or ethics where after millenia of argument there is still not enough agreement on the fundamental principles for them to become 'sciences' (but we hope there will be some day), or those whose work doesn't fit neatly into one field, or who can't confine themselves to a single field, etc. You will also notice that according to my definition those who don't believe in any definition of 'truth' (as, e.g., neo-pragmatists) cannot be philosophers. My apologies to Richard Rorty.
Charles Kahn gave an excellent more extended definition of what philosophy is how it is different from wisdom literature, etc., in his intro to ancient philosophy course, but, alas, my course notes are in Philadelphia and I am in Athens.