Jane Austen, in Pride and Prejudice, portrayed several things through her chosen title.
First, Mr. Darcy exhibits pride when he first arrives at Netherfield because he looks down on country society and refuses to join in on the dancing and games. Though not titled himself, because he comes from titled connections and is excessively wealthy, he considers the country gentry to be inferior.
Another example of pride in this book is exhibited by Lady Catherine de Bourgh. Lady Catherine exhibits a great deal of pride because of her wealth and title. Her pride causes her to look down on Mr. Darcy's, her nephew's, marriage proposal to Elizabeth Bennet.
A third instance of pride is exhibited by Mr. Collins. Mr. Collins is especially proud of his position at Lady Catherine de Bourgh's parsonage, hence when it is learned that Lydia has run off with Wickham, instead of responding with empathy or compassion, he claims that the Bennet family is no longer worthy of his association.
Finally, Elizabeth is the main character who displays prejudice. While it may be true that Mr. Darcy acted with great pride, Elizabeth allowed herself to become prejudiced against seeing his better nature. Her prejudice allowed her to think the worst of Mr. Darcy and side with Wickham. Instead, Mr. Darcy proved to be the most generous, kind-hearted man she had ever met.
The title is, in a sense, ironic. In the novel, as Elizabeth starts thinking about Mr. Darcy's first proposal, she realizes that her initial understanding of pride and prejudice is in need of revision. As Elizabeth is the viewpoint character of the novel, Austen expects that readers, too, will rethink these terms and gain some degree of wisdom along with Elizabeth.
Initially, Mr. Darcy is the emblem of pride, a wealthy gentleman who appears to scorn unsophisticated provincial life and people less wealthy and cultivated than members of his own family. He is contrasted with the more genial Bingley. Elizabeth, on the other hand, appears to be prejudiced against Darcy, initially because she overheard some rather disparaging remarks he made about her. Elizabeth's rejection of Mr. Collins can also be seen as a certain type of prejudice, as can her reaction to Charlotte's quite sensible acceptance of him.
Eventually, though, Elizabeth comes to understand that her own actions derive in part from her pride in her own cleverness. She also begins to understand that some of Darcy's pride stems from his sense of duty to the responsibilities he took on at a young age and that this pride causes him to be an excellent landowner and master to his servants.
Mr. Collins and Lady Catherine de Bourgh show extreme pride in their situations and Lady Catherine also displays a considerable degree of class prejudice.