Genre and subgenre definitions can be both confusing and contentious.
Or we can have fun with all our differences. Thanks to game designer Steve Ince for pointing out these two handy guides to genre in his blog:
These folks have inspired me to create this
Handy Guide to Science Fiction and Fantasy Subgenres
Science Fiction subgenres
Hard Science Fiction: playing with AI, genetic engineering and matter-energy transference.
Military Science Fiction: playing with ginormous space warships
Colonial Science Fiction: playing on alien planets
Space Opera: playing with blasters and rocket ships
Space Western: playing with sixguns and rocket ships
Steampunk: playing with dirigibles and shiny brass steam engines
Alternate History: playing in the Confederate States of the Third Reich
Time Travel: playing with the Tardis and the laws of Relativity
Cyberpunk: playing havoc with the Establishment’s computer networks
Dystopian Science Fiction: Big Brother doesn’t allow playing
Post-apocalypse Science Fiction: nothing left to play with
Epic Fantasy: playing with heroes, elves and evil overlords
Urban Fantasy: playing with immortal critters in the sewers
Dark Fantasy: playing with magic that might or might not cost your soul
Sword and Sorcery: playing with big swords and tiny garments
Magic Realism: playing with ordinary life through a really warped mirror
Paranormal Mystery and Romance: playing with vampires, werewolves and ghosts
Superhero Fantasy: playing with capes, tights and heat vision (or is that erotic fantasy…?)
For more serious reference, the definition-defying genre books site Worlds Without End has a much longer list of subgenres, with popup definitions (which I have ignored because actual definitions might affect the silliness). I notice their list forgot steampunk!
And please do suggest more subgenres and definitions if you have them!