There are at least two senses in which the term philosophy is used: a formal and an informal sense. In the formal sense, philosophy is an academic study of the fields of aesthetics, ethics, epistemology, logic, metaphysics, as well as social and political philosophy. One's "philosophy of life" is philosophy in the informal sense, as a personal philosophy, whose focus is resolving the existential questions about the human condition.
The term also refers to a specific conception of philosophizing as a way of life, endorsed by the German Lebensphilosophie movement whose main representative is Wilhelm Dilthey and several other Continental philosophers such as Henri Bergson and Pierre Hadot.
The human situation appears to be a struggle between what is (existence) and what ought (essence) to be.
There are at least three prevailing theories on how to respond to the existential question.
There are two basic forms of existentialism:
Religious existentialism is best exemplified by St. Augustine, Blaise Pascal, Paul Tillich, and the philosophy of Søren Kierkegaard. Religious existentialism holds that there are two levels of reality, essence, which is the ground of being, and existence. Religion is the ultimate concern in this view.
Atheistic existentialism is best exemplified by Friedrich Nietzsche, Martin Heidegger, and Jean-Paul Sartre. It holds that there is one level of reality, existence. In this view, each person constructs his own unique and temporary essence.