What is a doctor?
a doctor is usually someone in the medical profession, who has received the proper education and license to practice.
however, a doctor in general is someone who has received a "doctor's degree" from a university.
A PhD is awarded in a variety of disciplines to someone who has written a dissertation and generally added to the accumulated knowledge in the field, or shed new insights into that knowledge.
A DDS is awarded to one qualified in dentistry
An MD is for those in the fields of medicine practiced on people
a DVM is a doctor of veterinary medicine, for animals.
And the are other specialized doctorates as well.