Loners are those who like being left alone to be on their own. They are always happy staying away from a company and intentionally avoid interaction with people. Some loners who are considered extreme often go as far as loving away from town or places with a dense settlement.
Loners have some traits of introverts but they are more like advanced introverts. Sometimes loners go for events but definitely will go alone and would still not interact.
Dating loners can often be difficult. Sometimes it is hard for people to understand that loners are happy being with themselves. To date them, you need to prepare your mind to put up with that loner personality they have.
All in all, loners exist and they are humans. Do not despise them because some of them are quite nice.