An instinctual / intuitive (inner) personal connection with an animal or animals. the connection could also be experienced / interpreted as spiritual or mental. for example, it said that therianthropy is the connection to the animal spirit and nature.
I would say one is born a therianthrope, yet may not understand or recognize their 'other' nature until a specific event, usually related to the animal(s) awakens them to the fact. From then on it is more pervasive and prominent, just as much a part of themselves as their human body (no matter what kind of shifting is involved), which is experienced differently by each individual. It is commonly thought that a person can't become a therian, but can awaken to the fact or remember things.
With this comes an intimate connection with the natural world to varying degrees. Being a specific animal, knowing what it's like to be the animal, gives an altered, usually more 'primitive' (different than human) view of the world. One, I would say, that the person feels extremely comfortable having, if not being just as real to them as their human side.
At times, when one mentally shifts, the only way that could describe the experience is by associating it with a specific animal(s) (as opposed to pretending or trying to be (like) an animal).
Confusion, fear and doubt are some emotions that a therian might experience because of the conflicting natures. Though doubt (of being something other than human and doubt of being a specific animal(s)) usually lessens as a person delves more deeply into what it means to be therian.
By: SD Wolf
Therianthropy is the belief that one is, in whole or in part, one or more animals in some manner other than physically.
A mental, religious, spiritual, physical, or emotional connection or empathy with an animal.
I would add, personally, to the above definitions, that the connection would need to be more than the garden variety "I like cats" or "animals are neat and I love them", but those are my words, and I won't put them in anyone else's mouth.
Please do not mix the above definitions with your personal definition... this is something I think lots of input on would be good. You can however, add your personal definition below them and label yours as such.