In general, conflict is what results when someone trying to do something runs into opposition or an obstacle. My dictionary, Webster's New World Dictionary of the American Language, Second College Edition (New York: Simon and Schuster/Prentice-Hall, 1986) defines "conflict" as "1. a fight or struggle, especially a protracted one; war 2. sharp disagreement or opposition as of interests, ideas, etc.; clash 3. emotional disturbance resulting from a clash of opposing impulses or from an inability to reconcile impulses with realistic or moral considerations." It also offers a number of synonyms, each with a slightly different connotation: fight, struggle, contention, and contest. My thesaurus, Roget's International Thesaurus, Third Edition (New York: Thomas Y. Crowell Company, 1962), offers seven general references (to groups of synonyms) for "conflict" as a noun: contrariety, counteraction, opposition, disaccord, contention, contest, and hostility. Just one of these, "contention" offers two full columns of synonyms. An obvious conclusion one could draw from this is that, whatever "conflict" means, there is an awful lot of it in our lives. But I'll go one better than that: conflict is inescapable--at least while we are alive--and is present in many forms every single second that we are living. Our muscles work by opposition; our breathing involves inhaling against resistance that is used to exhale; the electricity that keeps our hearts beating travels over a neural network of specific electrical resistance. Simply the act of standing up defies gravity. I could digress at length here, but I won't. Suffice it to say that there is conflict in every aspect of our lives at every level, and that while opposing forces may wax and wane, seldom is any conflict ever truly resolved.
In order to be true-to-life--in other words, to embody psychological realism--fictional stories must show characters in conflict. In order to be interesting to readers, stories must show characters attempting to cope with conflict. My dictionary defines "to cope" as meaning "1. to fight or contend with successfully or on equal terms 2. to deal with problems, troubles, etc." The character's success or failure may ultimately make us happy or sad, but it is his struggle that interests us, regardless of whether it resembles struggles in which we are engaged or not. It is the general idea of struggle that engages us because we are all engaged in struggle all the time, burdened by it frequently, joyous in our resolution of it sometimes, saddened by the resolution of it frequently. It is a character's struggle that enables us to identify with him or her. To be entertaining, however, the conflict must be somehow significant and of consequence to us--particularly emotionally. Even a story focusing on the difficulty of keeping the carpets clean in a 15 room mansion could be made entertaining to nearly all of us--if the writer enabled us to find some consequential aspect of the conflict to which we could relate. For example, we might have no interest in cleaning carpets, but we might identify with a never-ending struggle, particularly if failure meant losing a job, inability to feed a family, or raise enough money to accomplish some important goal.
Conflict has sometimes been described as "the glue that binds together the events of the story," or "the glue that holds a story together." Edgar V. Roberts, in Thinking and Writing about Literature (New York: Prentice-Hall, 1964, 1978), wrote: "The structure of a work may be seen in terms of oppositions or conflicts that continue throughout a work until the final resolution." ("The Theme Analyzing Structure," page 133). It is a writer's orchestration of attempts to resolve various conflicts that comprise a story, and ultimately the arrangement of those attempts aimed at resolving a particular conflict that work to evoke our concern and to make us anticipate the outcome that provides the "spine" on which the rest of the flesh and bones of the story is hung. In other words, (using a climactic story structure here as the example) the writer presents a set of events, ordered so that each event involves a character endeavoring to resolve an evermore consequential conflict, until ultimately the conflict is resolved positively or negatively for the character. This arrangement of events is generally called the plot. Note that the term "plot" simply means plan or scheme. A writer's plot doesn't always produce a climactic story, but that is probably the kind with which readers in general are most familiar.
Theme or meaning is generally discovered by the reader looking at several things: first, the nature of the characters and the conflict. Who the characters are and the kinds of problems they're having enable us to cut through the possibilities and come to some quick conclusions (not necessarily accurate) about them. Then we look at how these characters are going about resolving their conflicts and why the results are consequential to them. Next we look at how the characters change or change their environment in the process of resolving their conflicts. Of course, it's not always the main conflict that is the key to understanding the story. Sometimes the kinds of minor conflicts, and how he goes about resolving them, are more revealing of both character and meaning. Say two men are trying to find a treasure: whom do we root for? The wealthy industrialist who simply wishes to add to his acquisitions or the young man desperately seeking the finances to pay for the operation that might save his sister's life? The answer might not be so clear cut if we could see the industrialist playing by the rules, doing generous and kind things for others with his money, supporting perhaps the very hospital where the girl will have her operation, and if we could see the young man cheating, gambling away money that could have paid for the operation, pushing out of the way other contenders for the treasure that might be equally deserving.
Robert McKee, currently the most respected screenwriting guru in America, is adamant and unequivocal in his assertion about the importance of conflict in a story, a statement that he calls the "Law of Conflict:" "Nothing moves forward in a story except through conflict." What he is saying, essentially, is that it is not logic but our concern for the characters and their struggle that affects us emotionally and involves us in the story. "Put another way," McKee says, "conflict is to storytelling what sound is to music. . . . As long as conflict engages our thoughts and emotions we travel through the hours unaware of the voyage . . . . But when conflict disappears, so do we." (Story. New York: HarperCollins, 1997, page 210-211)
Rust Hills, once the fiction editor of Esquire magazine, in a small volume published 26 years ago entitled Writing in General and the Short Story in Particular, intended for writers and would-be writers wrote: "Considered for the moment . . .purely as a plot device, conflict leaves a good deal to be desired when it is made the main structure of a story." What he meant was that external conflicts must be internalized somehow "if the outcome is to have any significance at all. The outcome must be made to depend on the character's will . . . . The outcome of plot must have some relation to character." (Boston: Houghton Mifflin, 1977; Bantam edition, 1979, pages 31-32.)
Most literature texts will tell you that there are five basic kinds of conflict:
Man vs. himself
Man vs. man
Man vs. Society
Man vs. Nature
Man vs. God or Fate
There is, however, an infinite variety of subtypes. For example, a character may have some psychological aversion to something that he has to do; he may need to do something requiring delicate physical maneuvering, but he is clumsy and inept; he may need to be serious, but he has an indomitable sense of humor, and so on. Also, while one type of conflict most likely will be dominant in a story, it is likely that the character is involved in several kinds of conflict--often all at once. One should note that all but one of these types of conflict is external. Man vs. himself is an internal conflict. What Hills was saying is, regardless of the kind of external conflict, in order to achieve significance it has to put a character into conflict with himself. And whether the conflict ever achieves significance of any kind generally depends on the extent to which theme is important and character change--as the result of character choice--is necessary. Some stories are designed to entertain through excitement and suspense without much regard to what the events might mean. When we read them, we discover that most of the conflict, if not all, is external. We generally call such stories plot-driven because we are only or primarily concerned about what happens and there is little or no change in the main character from beginning to end; the character learns or discovers little or nothing, and the events have little or no meaning or significance to the character. Enough action/adventure stories are of this type that they are usually what we think of first when someone says, "plot-driven." But watch out for stereotyping genres: not all action/adventure stories are exclusively plot-driven, and any type of story can be. In stories written in the last half of the twentieth century, and occurring with greater frequency as one nears the present, there has been an increasing tendency to emphasize both plot and theme in all kinds of stories--perhaps the result of a growing awareness among readers and writers that everything that happens affects us internally as well as externally.
"The Writer's Encyclopedia," found online at the Writer's Market site, offers a great deal of information of use to both readers and writers. Go to: http://www.writersmarket.com/encyc/c.asp and scroll down to learn about conflict.
For an interesting discussion of conflict, go here: http://www.writersmonthly.us/pages/wm_library/essays/is_conflict_necessary.html
I confess that I'm not totally in harmony with writer Christopher Mahon's point of view in the article cited immediately above (My belief may have more in common with those of Lee Zion, the writer of a rebuttal to Mahon's essay also displayed on this page.), but Mahon does touch provocatively on many aspects of conflict that both writers and readers of fiction need to consider.
Here's another useful discussion of conflict: http://www.fictionfactor.com/articles/conflict.html