The Oxford English Dictionary defines philosophy as:
"1. The love, study or pursuit of wisdom, or of knowledge of things and their causes, whether theoretical or practical.
2. That more advanced study, to which, in the mediæval universities, the seven liberal arts were introductory; it included the three branches of natural, moral and metaphysical philosophy, commonly called the three philosophies."
natural philosophy = science (the knowledge or study of natural objects and phenomena)
moral philosophy = ethics (the knowledge or study of the principles of human action or conduct)
metaphysics = that department of knowledge or study that deals with ultimate reality, or with the most general causes and or principles of things
Metaphysics gets the prize here for being the least clear definition. I will return to this topic later.