Here is the definition of the term provided by the subreddit forum PortalFantasy.
“Portal Fantasy is a fantasy subgenre term for the purpose of describing a category of fiction that focuses on characters who end up in another world. These characters can be transferred in a variety of fashions and are often forced to leave their old worlds behind permanently.”
It is a genre that has been around for a long time in various forms. Think of ‘Alice in Wonderland’ by Lewis Carroll, or ‘The Chronicles of Narnia’ by C.S. Lewis. Both are early examples of how the genre was formed.
Modern stories have taken the idea and run with it. Now we have Portal Fantasy stories that crossover with SciFi, High Fantasy, Epic Fantasy and more.
Here are two recent examples of books/series that conform to the genre. One from me, and the other was something that I read recently and enjoyed.
The Dungeon Alaria By Joshua Kern (The MC and his House are transported to the world of Alaria during the onset of the apocalypse on Earth.)
Orphan Wars by J.N. Chaney & Scott Moon (The MC is transported through a device on the moon.)
Now, as I said before, this is clearly not the end all be all of a list. It barely counts as a list, actually. I just wanted to give a couple of examples so people understand what they are getting into when they read Albion in the future.
The Portals of Albion, is my current project and it mixes lite-Litrpg/Gamelit aspects with Portal Fantasy on a near-Earth world.