A community is a group of individuals who are joined together by some commonality, either a common interest, a common physical location, a common belief. I suppose ultimately what is required if you don’t have a common physical location is the ability to communicate.
For example there are these folks called the Furries who like to dress up and adopt the personas of plushy toy animals. 50 years ago if you had this fetish and were living in Iowa you would have shut up about it and never known about the Furries in North Carolina or elsewhere. Thus no community. With the internet you can start to have a community centered around this common interest and can even have annual conventions where you dress up like stuffed animals, or anime, with 3,800 other like-minded individuals.
By the way, I am a member of a poker playing community that has a common interest in losing money, a common location — the Baltimore area — and a common belief that gambling is a noble pursuit.