If this is what you are hearing from your veterinarian then it simply means a overall exam of your pet. Usually this is for new puppies or new dogs, but can be done to make sure they are up to date on shots and have no new health issues.
PET is the anagram for "Positron Emission Tomography", a usual full body exam using a radiologic element or "tracer" to scan for diseases in the body. Painless.
