What is high fantasy? It's a subgenre of fantasy which is set in invented or parallel worlds. The fantasy's world differs from the real world in various ways.
There are three types of high fantasy:
1. The fantasy world may have no connection to our world, as in the Valdemar series by Mercedes Lackey.
2. There may be a portal from the fantasy world to our world, as in the Narnia series by C. S. Lewis.
3. Or the fantasy world may be a world-within-a-world within the real world--- as in the Harry Potter series, where the wizarding world is within our own, real world.
In addition, there is a science-fictional subtype of type 2, where the 'portal' between worlds is in the form of spaceships and other technological means. This is how I would classify the Darkover series by Marion Zimmer Bradley. I also see the Homecoming series by Orson Scott Card, while it is seen as a science fiction series, as being somewhat like Darkover, a variant type 2 fantasy.
These distinctions are only important so far as it helps readers discover more books-I-like, and writers to find an audience.
My Wildmage series is High Fantasy type 2 (though I'm not sure the portals will play much of a part in the current book, it is how the planet was settled by humans.)