What is a PhD and why are they called doctors?

PhD stands for Doctorate of Philosophy, and is awarded in every field from English to physics. You can get a PhD in almost anything, but first you need a bachelors degree and a masters degree (usually in the same field as you want to get the PhD). So that's 8-12 years of college on average. It's a research degree, which means you got it by doing an original research project in your field, and you can do and publish original work. You need a PhD to teach at the 4-year college or university level.

PhDs were the original doctors (doctor is Latin for 'learned teacher') and the term 'doctor' was extended to the medical profession as a courtesy (although a medical doctor does not have a PhD) about 100 years ago; although now the term doctor implies medical doctor, it is still the correct form of address for someone with a PhD.