That simply means that on "an individual basis" the owner will consider pets.
Often an owner may be ok with a small dog, cat, etc, but perhaps may not have interest in "Gigantic Dogs", Mountain Lions, Sheep, Man-eating snakes or other "more crazy things" that some people consider as pets.
A little humorous there, but basically, they are just saying, "Let us know what type of pet you have, and we'll let you know if we will consider it". Sometimes an extra pet deposit may be required as well. Hope that helps.
Brian Luce ABR SRS