Often people try to describe a style of literature with a single range or spectrum from one extreme to another based upon a single element of the style. To the best of my knowledge, this is most often done in science fiction. This may be because science fiction fans like categorizing things, or they are just nuts. I hope that I fall into the first category.
Most often the category is based upon the question of how realistic of the science is - at one end of the spectrum there you have the hard science fiction authors dominated by Robert L. Forward, Stephen Baxter, and Gregory Benford to name a few of the modern authors. At the other end you have books that take place in the future but are more akin to the fantasy novels where technology takes the place of magic.
Some examples of this 'classic' hard/soft distinction can be seen in debates between Babylon 5 and Star Trek - The Next Generation. Within B5, the rules of the universe are rather well enforced from the configuration of the Starfury (the one or two man fighters) having thrusters placed at right angles with respect to each other for proper turns in space (and those that go into the atmosphere needing an airfoil) to the use of centripetal forces to simulate gravity on large ships and space stations. This differs from Star Trek with the particle of the episode, the way the ship turns (banking on what?), the mysterious everything interacts on the same plane rule, and a whole host of other things. This is not to say that one is better than the other (that debate is an ugly one) - the point is more of one of two different styles of science fiction that are well known and demonstrating a few key points from these.
This is by far not the only 'range' in science fiction. Another aspect to consider with respect to science fiction is that of "how much does the plot rely upon the essence of what makes the story science fiction?" For those who have read Robert L. Forward's books, it appears that the story is a science paper of some sort with a plot to it (Dragon's Egg - life on a neutron star, Flight of the Dragonfly - solar sail and tidal mechanics, Timemaster - wormholes and negative matter). This is not a bad thing; it's just his style of writing - one that some people would find rather dry (I tend to like it). On the other hand, you've got Kim Stanley Robinson and Nancy Kress, both of whom would be similarly classified as hard science fiction authors - just as Robert L. Forward is - in that they both strictly obey what science is and does without making up technology that cannot exist. However, both of these authors use science more as the backdrop for a larger human story - an excuse for "what if? how would this change human society?" By far, the master of this area of science fiction is Arthur C. Clarke with the masterpiece 2001 (this is not to say his other works are not masterpieces) that deals with human interaction, human computer interaction, and our place in the universe.
Looking at the softer (this is not to say that there is 'soft science fiction', but rather that it is not as 'hard' as 'hard science fiction') side of science fiction, one sees such authors as Robert Heinlein and Spider Robinson who are writing stories of human interaction. These stories most often take place in the future (though Spider Robinson's are often located in the 'now' but play with the elements of science fiction). However, this is most often just as a backdrop to the story. No attempt is made at trying to explain the technology or have it strictly conform to physics as would a hard science fiction writer would. The stuff that makes the story science fiction are used as plot devices. Laser guns? They work. FTL travel? It works. Generation ships run with punch cards? Yep - it was written in the 50s. The key point to recall understand is that this is about human interaction, no matter how silly the science or the story (especially the case with Spider Robinson) may be.
The astute reader may note that I have mentioned some of the greats of the modern era of science fiction but have failed to mention Isaac Asimov. This is primarily because of the difficulty that I have in classifying his works. The universe that Isaac Asimov writes in contains robots with positronic brains and a branch of math that can be used to predict the course of human society. Aside from these two aspects, he does not concern himself with the rest of technology as a hard science fiction author would. His stories often focus on these two, but yet the essence of the Robot series is how robots fit into human society, and the branch of math is about how human society works. Quite frankly, an argument to place Asimov in any section of this attempt of categorizing science fiction can be made - both for and against.
And failing again to mention a well-known science fiction author, I take this opportunity to point out the failings of any attempt to classify science fiction. Larry Niven is well known for his Known Space universe - one that includes Ringworld, the Puppeteers, and Louis Wu. This universe is fairy well defined with respect to it being hard science fiction - the General Products hull, tidal effects of neutron stars, Bussard ramjets. While science is fairly well explored, Larry Niven often looks at the aspects of the interactions between alien species - the warlike Kizinti, the paranoid Puppeteers, mind controlling Slavers and all manner of other species. In the Integral Trees and Smoke Ring, Larry Niven deals with the loss of technology along with humans living in a microgravity environment - and the interactions this produces between different cultures. It is hard to say that Niven focuses on technology or interaction, as do other writers.