The show was famously described as "the show about nothing," and such comment is largely accurate, as most of the comedy was based around the largely inconsequential minutiae of everyday life, often involving petty rivalries and elaborate schemes to gain the smallest advantage over other individuals. (The characters have also been described as utterly selfish and amoral, and to the degree that is accurate, the show stands out in deriving nothing but amusement from it.) However, themes of illogical social graces and customs, neurotic and obsessive behavior, and the mysterious workings of relationshipss run in numerous episodes. It follows the times. The show is also unique in reflecting the activities of real people, rather than the idealized escapist characters often seen on television.
In episodes adhering to the original concept, the show features clips at the beginning and end of each episode, with Seinfeld himself delivering a standup routine that ties in to the events depicted in the story. It is probably worth mentioning that in this sitcom, the distinction between the actor Jerry Seinfeld and the character who is portayed by him in the eponymous sitcom is therefore blurred; the character transcends his role. In later seasons, these standup clips were less frequent.
Another violation of the normal fiction convention of isolating the characters from the actors playing them, and the characters' world from the actors' and audiences' world, was a story arc that focused on the characters' roles in promoting a television sitcom series named "Jerry" ("about nothing") in which Seinfeld plays himself.
Another thing that makes this sitcom stand out from the rest is that the action within almost every episode is both dense and very well built around itself. Several threads of action are presented at the beginning of an episode, generally happening to distinct characters in the show independently, only to either converge or get interwoven throughout the episode. A nice exercise in this direction is to try to summarize the action in a random episode of the show reasonably accurately -- it generally proves to become a lot longer than expected.
Jerry Seinfeld (played by Jerry Seinfeld) - a reasonably successful standup comedian, who seeks out relationships with attractive women which rarely last more than one episode. A number of episodes involve some obsession of Jerry's that results in offending the romantic interest and breaking the relationship. Another favourite obsession of Jerry's was that of Superman and Lois Lane. There is a reference (visual, conversational, or thematic) to Superman in almost every episode of the series.
Cosmo Kramer (played by Michael Richards) - tall, wild-haired, Kramer is the Seinfeld character with the loosest grip on reality, decorum, or concepts of property. He is based on Larry David's sometime neighbour, Kenny Kramer.
Elaine Benes (played by Julia Louis-Dreyfus) - like Seinfeld, much of Elaine's life revolves around trying to arrange relationships with attractive individuals, although some of hers last rather longer than Jerry's. She has held jobs for Pendant Publishing, The J. Peterman Catalog, and as a personal assistant to Mr. Pitt. Elaine was a composite of two girlfriends of the creators.