Common terms for these animals: Emotional Support Animal (ESA), Comfort Animal, Companion Animal, Therapy Animal.

She moved in her sister, who then got a puppy and a letter from a therapist saying the dog is a companion to her. 

In particular, can I refuse to rent to certain protected classes like those with "companion animals"?

The Florida State Legislature is considering a pair of companion bills in the House and Senate that are intended to, amongst other things, preempt the regulation of vacation rentals to the state, but even if they were to pass, preemption would only apply to municipalities that did not have their own vacation rental regulations in place prior to June 1, 2011.

I work in a companion position to commercial real estate appraisers and as such have had opportunity myself to conduct title searches - one of the houses I mentioned earlier was also an estate property that had been flooded while the relatives sorted the will. 

It teaches you about MN law, and they have a companion book. 

If the tenant has a disability they can call it a companion animal.

We also use one card per property, generally and qualified easily for free companion pass on Southwest.

@Kevin Elguer Correct, together with two companions we are investing in Barcelona and Valencia at the moment.

However, if you love or even like travel, the points cards are a no-brainer: Free travel, food, lounges, booze, concierge service, companion passes, car / trip insurance, etc.