The question of what philosophy is, could generate numerous unsatisfying answers. Some would say that philosophy is one's "worldview"...but since everyone has one of those, than how is the actual study, and more importantly, the practice, of philosophy unique such that it deserves it's own term (and university degree)? Is it the "Love of Wisdom", as the etymology of the word "philosophy" would suggest? But that is somewhat vague...seeing as how we would clearly need some definitions of the "wisdom" (and not to mention "love"). The famous 20th century philosopher, Bertrand Russell, may have pointed us in the right direction with the following statement:

"Philosophy... is something intermediate between theology and science. Like theology, it consists of speculations on matters as to which definite knowledge has, so far, been unascertainable; but like science, it appeals to human reason rather than authority, whether that of tradition or that of revelation."---Bertrand Russell

 

And it could follow that philosophy is best defined not by what it is, but by what it does. And what philosophy does is attempt to reasonably provide answers for special questions called "fundamental questions". Fundamental questions arise in every area of learning---from education, to medicine, to science, to psychology, etc.. And they are such that they cannot be answered by appealing to empirical facts (they cannot be verified, or falsified by observation. These questions can be (philosophically) resolved by determining what is most reasonable to believe.

Below are videos that will demonstrate Western humanity's historical attempt to resolve various famous fundamental questions and how those answers have either determined or deeply affected the development of human cultural, religious, and political structures...while honoring and celebrating the various rock-stars of philosophy. Could you be next? You could be, but if bringing something new to the table is important to you, then it could be necessary to know what has come before....

The view from 10,000 feet: A history of philosophy, and it's sub-fields defined

Logic:
What is Logic?   Fallacies to avoid in Philosophy

Rock Star Philosophers throughout the ages:
About this list​, Socrates, Plato, Aristotle, Augustine, Thomas Aquinas, Niccolo Machiavelli, Desiderius Erasmus, Thomas More, Francis Bacon, Rene Descartes, Thomas Hobbes, Blaise Pascal, Baruch Spinoza, Gottfried Leibniz, John Locke, George Berkeley, Voltaire, David Hume, Thomas Paine, Mary Wollstonecraft, Jean-Jacques Rouseau, Immanuel Kant, Friedrich Wilhelm Josef von Schelling, G.W.F Hegel, John Stuart Mill, Edmund Husserl, Soren Kierkegaard, Martin Heidegger, Albert Camus, Karl Marx, Charles Pierce, John Dewey, Friedrich Nietzsche, Jeremy Bentham, John Stuart Mill, Bertrand Russell, Ludwig Wittgenstein, Simone de Beauvoir, Jean-Paul Sartre, Sir Karl Popper, Thomas Kuhn, AJ Ayer, Ludwig Josef Johan Wittgenstein, Michel Foucault, Jacques Derrida...

Particularly relevant for our times: Integral Theory

A catalog of philosophical ideas: Aristotle's Syllogisms, Russell's Paradox, Frege's logicism, Hume's problem of induction, Popper's conjectures and refutations, Kuhn's scientific revolutions, Descarte's Mind-Body problem, Kant's categorical imperative, Mill's utilitarianism, Marx's historical materialism, Pascal's wager, Socrates' method, Plato's cave, Berkley's idealism, Kant's synthetic a priori, Hegel's dialectic, Jame's pragmatism, Moore's common sense, Wittgenstein's picture theory of language, Nietzsche's superman, Derrida's deconstruction, Heidegger's nothing, Moral Relativism, Sartre's bad faith...