2. Q: What is a service animal?
A: The 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 perform some of the functions and tasks that the individual with a disability cannot perform for him or herself. "Seeing eye dogs" are one type of service animal, used by some individuals who are blind. This is the type of service animal with which most people are familiar. But there are service animals that assist persons with other kinds of disabilities in their day-to-day activities.
http://www.usdoj.gov/crt/ada/qasrvc.htm