A PhD (short for Doctor of Philosophy) is the highest academic degree a person can earn at a university. Someone pursuing a PhD spends years (usually 4–7) becoming an expert in a very specific topic, then writes a long research paper called a dissertation that adds new knowledge to their field.

Despite the name, you don't have to study philosophy to earn a PhD. You can get one in chemistry, history, psychology, mathematics, or almost any academic subject.

Earning a PhD means conducting original research: discovering something new that nobody knew before. A biology PhD student might study how certain bacteria survive in extreme cold. A history PhD student might uncover new information about ancient civilizations by examining old documents that previous scholars overlooked.

Once someone completes their PhD, they're called “Doctor,” though this is different from medical doctors who treat patients. Many people with PhDs become university professors, conducting research and teaching students. Others work in government laboratories, technology companies, or research institutions. A PhD represents the highest level of expertise in a subject, showing that someone can ask important questions, investigate them thoroughly, and contribute genuinely new understanding to human knowledge.