Pride and Prejudice is a social satire because its main themes, which are a) courtship, b) the need for marriage, c) women's lack of social ranking, and d) the division of social classes are mocked throughout the novel by presenting characters which are stereotypical of such themes in awkward situations.
Austen clearly uses her own voice through Elizabeth to explain her own views of these main themes: Why should women marry just to get financial stability? Why the extreme respect to the aristocracy? What's with Darcy's proposal? How DARE Mr. Collins propose? All these things are presented in a complex yet funny way because the characters produce the reaction.
In Mr. Collins we see the extreme bender for the aristocratic Lady Catherine.
In Lady Catherine we see the extreme, self-serving aristocrat who expects the world to bend to her.
In Bingley we see the weak, and easily manipulated upperclassman.
In Darcy, we see the snobby and full of himself aristocrat who even insults Elizabeth AS he proposed!
In Mr and Mrs. Bennet we see every reason why people should never marry.
In Lydia we see the extremes of how social opinion changes of you just for becoming a married woman.
In all, it is entirely satirical and completely interesting.