These definitions are my own and are not official in any way. If you question a definition, go ahead and challenge it in the comments. These are in no way final and are subject to change per your own definitions and what you see on a bookshelf.
Science fiction written for a teenage audience. Characters are typically in their teenage years and deal with teenage problems in addition to the problems of the world. The characters also make decisions a teenager would make, which aren’t always the best choices.
Across the Universe, Ender’s Game, The Hunger Games
The events of a plot take place within an imperfect society. Usually, the characters acknowledge that their world is imperfect and go on to challenge the world, which can often reflect on the current state of society (in that we acknowledge the world is immoral and unjust and challenge it every day). In a true dystopia, however, the characters AND reader don’t realize their society has major structural issues until they make a discovery of some sort.
The Giver, Anthem, 1984
Apocalyptic fiction takes place during the apocalypse. It often tackles the question of how the world is changing and how people deal with it. I prefer apocalyptic fiction to be absolutely terrifying.
Life as We Knew It, Y: The Last Man
Post-apocalyptic fiction takes place after the apocalypse. Also tackles questions of how characters cope with the world, especially when it used to be so different. Plots the changes society makes as a result of the apocalypse. Often crossovered with the dystopia subgenre. I find nothing wrong with the crossover, but sometimes its refreshing to see one genre without tropes from the other.
Ariel, The Road
In which the main action takes place across several planets, often in a universe where intergalatic space travel is as common as traveling to the next city on Earth. Often borrows tropes from the fantasy genre. Don’t let anyone tell you Star Wars is a fantasy. In fact, I would call this genre the epic fantasy of science fiction: there’s so much people think of this when they think “science fiction.”
Star Wars, Old Man’s War, A Fire Upon the Deep, Catspaw
The main characters are part of the military and the military is the source of the main action and plot. Characters MUST know what kind of gun they’re shooting and what their gun can do. Interactions between various ranks must past a test judged by people who actually served.
The characters are the main driving force of the story. I see Spec Fic as the literary fiction version of science fiction. If you write speculative fiction, you may be an academic. Or perhaps you like the term better. You are allowed to group both science fiction and fantasy into the speculative fiction genre. I, however, like to call Speculative Fiction the science fiction of the literary and academic scene.
Margaret Atwood, Ray Bradbury,
The setting and society takes place within an alternate and/or fantastical version of the Victorian era. Can also transpose the values of the Victorian era into a different time, often far into the future. Technology is often steam-powered, airships abound, automatons are commonplace, and/or costumes are extravagant. Also an awesome costume theme.
Fitzpatrick’s War, Leviathan, Behemoth, Goliath, Jay Lake
In which the world is overrun with computers and/or something similar. Robotic or cybernetic implants are common for characters. The world is heavily based around technology.
The Matrix trilogy, Blade Runner, Philip K. Dick
Hard Science Fiction
A large portion of the story focuses on the actual science of how the world works. If you like the sciences, this is the genre for you. The science must be accurate otherwise you’ll have a team of fans and/or scientists on your tail for being incorrect.
Kim Stanley Robinson, Arthur C. Clark