Daisy Buchanan is one of the principal characters in The Great Gatsby by F. Scott Fitzgerald, and she is the cause of almost all the trouble that happens in this novel--and certainly the motivation for nearly everything Jay Gatsby has done in the past five years.
Daisy is married to Tom Buchanan. She is a rich socialite who married an equally rich man, and they quite deserve each other. Daisy had a chance to marry someone (Gatsby) for love (which she wanted to do mere hours before marrying Tom), but she made the shallow and expected choice and married Tom because that ensured her position in society and her wealth.
There are several distinguishing characteristics of Daisy Buchanan; one of them is that she always wears white. Another is her voice. It sounds, as Nick describes it, like money. She speaks rather quietly (low) so people have to come near her in order to hear what she has to say because she believes the world revolves and her. She is selfish and self-absorbed. The word which best describes Daisy Buchanan is self-absorbed.
She loved Jay Gatsby, but her parents did not want her to be associated with him. She chose money and position over love.
Gatsby knows this about Daisy, too, when he tells Tom:
“She only married you because I was poor and she was tired of waiting for me. It was a terrible mistake, but in her heart she never loved anyone except for me.”
She is the one who kills Myrtle Wilson and willingly lets Gatsby, the man she says she loves "now," take the blame for that. Her selfishness costs Gatsby his life.
She knows her husband has been cheating on her, even on their honeymoon, yet she stays with him because it suits her social status to do so. She is obviously unhappy and even hurt, but she stays.
Though we do get the sense that she once felt something for Gatsby and feels something for him again now, Daisy clearly does what suits her first and just ignores whatever does not suit her. She condemns Tom's affairs yet has her own. She puts Gatsby out of her life as soon as Tom makes more (presumably) idle promises to be more faithful to her. In short, anything that makes her happy is good; anything else does not exist for her.
The quote that best describes this quality in Daisy is said about both her and her husband. This is fitting because they really are the same kind of people, though it does not seem so at first. Nick says this about them:
"They were careless people, Tom and Daisy--they smashed up things and creatures and then retreated back into their money or their vast carelessness or whatever it was that kept them together, and let other people clean up the mess they had made."
This carelessness is rooted in her selfishness, as the only thing that matters to her is her. I describe Daisy as selfish or self-absorbed; Nick, who is her cousin, calls her careless. Either word correctly describes her.