Many people will use the terms interchangeably, but they are not the same thing!
Service dogs are dogs trained to perform a specific task to aid an individual with a disability. Service dogs access to public places is protected by the federal govt. under the Americans With Disabilities Act. Access is only granted when service dogs are in training or being handled by an individual with a disability for whom the dog has been specifically trained. Keep in mind that not all disabilities can be seen from the outside, and service dogs can be trained to perform many tasks for people who may not be in a wheelchair or display outward signs of a disability.
Therapy dogs are trained to provide comfort to many different people in many different positions. The medical and emotional benefits of pets have been well documented. Therapy dogs may also work with doctors, physical therapists, psychologists to help people. Therapy dogs may visit people in hospitals, hospice, schools and have even gone to court to provide comfort and strength to children who must testify. Therapy dogs right to public access is NOT protected by the federal govt. Therapy dogs must be invited into businesses, hospitals, schools and other medical facilities. Most of these places require therapy dogs to be certified by a third party.
Emotional Support Dogs are animals who provide comfort and emotional support to a specific individual who may suffer from anxiety, stress, phobias, depression, or any other form of emotional distress. These dogs are not protected under the Americans With Disabilities act and are not guaranteed public access. However, Emotional Support Dogs are federally protected to live in apartments, rentals or housing who may have limits on “pets”. Emotional Support Dogs are also protected under federal law to travel on airplanes with their owners. However, restaurants, malls, schools and various other public places are not required by law to permit Emotional Support Dogs. If you have an Emotional Support Dog, you may be asked to present a letter from your doctor stating you are receiving their care and that an Emotional Support Dog is necessary for you.
If you would like more information, I recommend you visit the A.D.A. National Network: https://adata.org/publication/service-animals-booklet