We've considered quite a bit the definition of "classic", and it's been interesting to hear.  For instance, one notion that has me musing a little is that of "modern' classics.  But what I'd like some of you to express your thoughts on is a not-too-loose definition of "novel".    I got to thinking about Death Comes for the Archbishop, by Willa Cather, and wondering what difference its lack of a 'plot' makes to its literary categorization?   Can there be 'novels' in which the author doesn't develop any plot-line, but does set forth characters and develop them, for example?  In the interests of disclosure, I'll admit I haven't thought much about this yet, but am sorta toying with the idea.

Out of curiosity I just pulled off a shelf a 12-pounder that calls itself, Merriam Webster's Encyclopedia of Lliterature.  The entry under classic gives anyone and everyone as much wiggle room as they want: 

A work of enduring excellence or the author of such a work.

The operative word, of course, is excellence. 

Nevertheless, I don't think you'uns will find me making a case for my H.S. favorites My Gun Is Quick and Battle Cry.

Yes, the definition of a "classic" is very subjective.

 What makes me smile is "modern classic". I don't recall seeing the term modern classic until some wily booksellers (Penguin comes to mind) started using the moniker to garner more interest in and sell more of their books. I may be wrong about this so if anyone else knows the origin of this term, please enlighten us.

Regarding character-driven novels, "The Sea" by Banville is another example. I don't believe a plot is essential to a good novel but if you don't have a plot then you should have some compelling characters and/or interesting relationships. Cather's Archbishop was compelling; Banville's widowed Morden was rather tepid IMHO.

Within the category of Literature and Fiction you have subgenres like Mysteries (heavily plot driven), Romances (relationship driven), etc.

I don't believe plot is essential to define something as a novel. My understanding (gleaned from the corner of my eye in my various social science courses in college) is that a novel is simply a long, fictional narrative in prose -- thus separating it from a short story (short narrative in prose), a history (which would be non-fiction), and any sort of poem. Some of the earliest novels had very little plot -- Tristam Shandy comes to mind immediately. Of course there are grey areas -- the long requirement always seems arbitrary (though I know there are in fact arbitrary lines drawn between novels and novellas, I just forget what they are right now and the novel that's exactly one page over novella length always makes me laugh), the fictionality can sometimes be extremely blurred (hello, historical fiction genre!), and the line between wonderfully poetic prose and actual poetry has gotten very confused (for me at least, but then I really require meter to enjoy a poem, so I haven't enjoyed a poem written anytime in the last century). Those're my off-the-cuff thoughts. :)