Yes, there is a distinction between "service" and "therapy" animals.
According to the U.S. Department of Justice , "The Americans with Disabilities Act (ADA)  defines a service animal as any guide dog, signal dog, or other animal individually trained to provide assistance to an individual with a disability. If they meet this definition, animals are considered service animals under the ADA regardless of whether they have been licensed or certified by a state or local government."
Service animals are trained to perform tasks that individuals with disabilities cannot perform for themselves, such as guiding people who are blind, alerting people who are deaf to alarms and other sounds, opening doors and picking up objects for those with mobility impairments, and alerting and protecting people who have seizures. They are also trained to behave properly in public places. As far as businesses and organizations that serve the public, the Department of Justice states that "the ADA requires these businesses to allow people with disabilities to bring their service animals onto business premises in whatever areas customers are generally allowed."
The duties of therapy dog are not limited to working with people with disabilities and are not legally defined. A therapy dog is allowed into locations, such as hospitals and nursing facilities, by invitation only, perhaps as part of a treatment plan. Some national and local organizations may certify therapy animals; however, even with certification, a therapy animal does not qualify for the access protection given to service animals under the ADA.
For more information about service animals, consult the Department of Justice publication entitled Commonly Asked Questions About Service Animals in Public Places of Business .
-  U.S. Department of Justice
-  Americans with Disabilities Act (ADA)
-  Commonly Asked Questions About Service Animals in Public Places of Business