Science Fiction is a genre of fiction that involves future technology or things that are interesting in theory but we wouldn't want to happen in reality. It usually contains a message to the readers, a theme, warning of the harmful consequences of the excessive use of technology.
--- adding ---
Hard Science Fiction is generally an attempt to predict what inventions will occur next and what their social impact will be on the human race. A good example would be "what if there were robots to do all our housework " , and then you get a movie like "I Robot" staring Will Smith showing half the population out of work because all the dead end minimum wage jobs got taken up.
Not to say that would really happen, merely the author speculating on the consequences.
Science fiction is a genre which is based on things that are in the future or that are not real, such as aliens, telepathy, etc.
corret