Michel Foucault first used the term to reference a place that is similar to terms such at utopia and dystopia in the fact that they resemble our world, but are different or separate from it in some way. Utopias are of course unreal places, they are just imagined and cannot exist due to their qualities. A heterotopia, however, can exist. They are spaces (as described in my previous post) that have a place in the real world.
Over time we have come to understand and label heterotopias in a different way. For now we exit in a time where spaces and worlds aren't always entirely real, and can exist in a virtual place. The term heterotopia is perhaps a more useful term now than ever before to try and help define the space that we live and exist in.