Otherkin are people who identify spiritually or psychologically as nonhuman, specifically beings who do not currently exist on earth (though it is often used as an umbrella term). Various kintypes include but are not limited to elves, demons, fae, dragons, angels, and many others. The otherkin community consists of: spiritual beliefs, such as your soul is nonhuman or that you were meant to be reincarnated as nonhuman in this life; and psychological ones, such as that your feelings are caused by an unconscious coping mechanism or that you are mentally closer to your kintype than a human.
There is overlap between Otherkin and Therians due to the fact that the two concepts are similar. Many consider therians to be a sub type of Otherkin as they use otherkin as an umbrella term for nonhuman identities. Because of this someone with a wolf soul might call themselves a wolf therian, wolfkin or both. Someone can also be both otherkin and therian, for example; a demonkin could also be wolf therian through having multiple kintypes.
Otherkin are often referred to as 'Kin for short. A Kintype/Theriotype is the animal/being the 'Kin identifies as. As stated above being Otherkin/Therian is very personal and beliefs of cause and experience vary from one individual to another. Some may believe their soul is a mixture of more than one species (hybridkin) and others may have more than one kintype (polykin). The otherkin community is a very diverse community that has many different beliefs and opinions.