Philosophy is defined as "the rational investigation of questions about existence and knowledge and ethics," or "a belief system accepted as authoritative by some group or school," according to Vocabulary.com.
Philosophy has Greek roots, where "philo-" means "love" and "-sophos" means "wisdom." People who study philosophy seek the meaning of life, and the meaning of life differs for each philosopher. While the definition of the word "philosophy" has one meaning, there are many philosophers and philosophies about the meaning of life.
Ancient philosophy's roots come from thoughts by Thales of Miletus, who is known as the first ancient Greek philosopher. Socrates, Plato and Aristotle are regarded as some of the most highly regarded philosophers in history. Friedrich Nietzsche, Thomas Hobbes and Auguste Comte are also well-known for their contributions to today's definitions of philosophy in society.