Clinical focus. Although both psyd and phd psychologists are trained in the care of those with mental disorders, psyd programs focus primarily of preparing the person to be a therapist and tester, whereas phd programs also teach research techniques and require a formal, completed research project for completion of training.
Doctorates. Both are doctoral degrees. There is often no difference in training.
Traditionally. Psychologists were given PhDs or Doctorates in Philosophy. More recently PsyD programs have developed training programs in applied Psychology, PsyDs. The training is all focused on applied psychology as a professional Doctoral Degree. There are only a few PsyD programs and most psychologists still have PhDs. .
Slight difference. Both have earned doctoral degrees focused on psychology. People who have Psy.Ds are doctors of psychology. Whereas, individuals with Ph.D.s in psychology technically have doctor of philosophy degree. In practical terms, people with either a Psy.D. or a Ph.D. can become licensed psychologists and they often do the same kind of work.
Research vs Clinical. A PhD is typically a research degree that emphasizes experimentation, time in the library, and publications with lesser of an emphasis on clinical work. A PsyD on the other hand, is a clinical degree that emphasizes work with patients instead of research quite so much.