A Doctor of Philosophy (PhD, Ph.D., or DPhil; Latin Philosophiae Doctor) is a type of doctoral degree awarded by universities in many countries. Ph.D.s are awarded for a wide range of programs in the sciences (e.g., biology, chemistry, physics, mathematics, etc.), engineering, and humanities (e.g., history, geography, literature, musicology, etc.), among others. The Ph.D. is a terminal degree in many fields. The completion of a Ph.D. is often a requirement for employment as a university professor, researcher, or scientist in many fields. A clear distinction is made between an "earned doctorate", which is awarded for completion of a course of study and a thesis or dissertation, and an "honorary doctorate", a title granted by a university to a successful or notable person who has not completed doctoral academic work or completed a dissertation at the university. Individuals with an earned doctorate can use the title of "Doctor" with their name and use the post-nominal letters "Ph.D.", "PhD" or "DPhil".
Source: https://en.wikipedia.org/wiki/Doctor_of_Philosophy