reference.com defines it as:
of, pertaining to, or characterized by a manner of writing in which a character's thoughts or perceptions are presented as occurring in random form, without regard for logical sequences, syntactic structure, distinctions between various levels of reality, or the like.
Wikipedia says:
Stream-of-consciousness writing is usually regarded as a special form of interior monologue and is characterized by associative (and at times dissociative) leaps in syntax and punctuation that can make the prose difficult to follow...
Basically, stories or speeches written in this style tend to go on and on and reflect the writer's or character's feelings without regard for the reader's sense of structure or sanity. They will go off on tangents, and even their tangents spawn tangents of their own, and you never know quite where they're going, or what the whole point is. If you've seen the show Scrubs, you've heard stream of consciousness whenever J.D.'s mind speaks to the audience. Though in this case, it's not nearly as long or meandering as the term connotes.
Let me just say that I'm glad I left English classes behind in high school. If I am forced to read and analyze anything (more) done in stream of consciousness, I'm going to go crazy (or at least get a headache). But I came to a realization today.
I now know why I hate my math class. It's not because it's an upper division linear algebra class: I actually liked my lower div class in the same subject. It's not that the book contains so many theorems and definitions that one cannot hope to memorize. It's not centered on the fact that the dozens of proofs try to make me think in a way that I'm not used to thinking. It doesn't even bother me that the professor is an old Japanese guy who speaks with a considerable accent. I hate my math class because in each of the three lectures I attend every week, the professor engages in stream of consciousness math.
That's right, when writing all the symbols and equations and expressions on the board, he frequently displays leaps in syntax, punctuation, and logic that make his ideas incredibly difficult to follow. He goes off on tangents regarding how math people are smart and should be able to use their brains to find little tricks to solve otherwise long, laborious problems (my word, not his). Never mind the fact that these tricks are so intricate and off the wall that I wonder if a single person other than him actually gets it.
So while the class stares agape at the nonsense scribbled on the chalkboard, he flashes his customary toothy grin and says "so... in otha word..."
moving to a clear section of the board..
"in otha word..."
Then he fills nearly another whole section of the board with more gibberish before we are able to recover and finish writing stuff from the other section... our lack of understanding of the material to begin with notwithstanding.
He just goes on and on for 50 minutes, and I leave each lecture with a few more pages of sloppy, messily-written notes regarding who knows what. In other words... in other words... WTF?