There are as many definitions for 'philosophy' as there are philosophers. However, this does NOT mean it is just a matter of personal opinion. A good definition of 'philosophy' aims to capture it as a deliberate and intentional method / approach to solving problems.
The evolution and development of all other disciplines (including theology) could be understood as the result of having arrived at answers to some of these fundamental questions. As such, it is fitting that the first institutions of higher learning were built by and for philosophers, and that no matter what academic discipline one major's in, the highest degree possible is a PhD (i.e., Doctorate in Philosophy).
Thus, one might best define Philosophy as the Mother of all Questions; or as it is more literally translated, "the love of wisdom".
The Basics
Laying out a worthwhile "philosophy of ... [fill-in-the-blank]" requires one to provide both necessary and sufficient reasons to believe the plausibility of one's claims (i.e., good / persuasive reasons to think something is the case).
Study of general and fundamental problems in the form of questions. Whether inside or outside of academia, this intellectual activity, when done well, promotes a boundless way of engaging in the world.
ANYONE can be a philosopher, though that hasn't always been acknowledged
Like most institutions of authority, women and POC have been excluded and erased from the History of Philosophy. “The habit of ignoring female philosophers has become so entrenched that even the secondary literature is marked by their absence.” (Weinberg)