Seinfeld was essentially "The Show About Nothing." Following a group of four friends, the show focused on the most mundane and simplest #whitepeopleproblems to ever exist.
Episodes were filled mainly with interactions with strangers, but there were many returning characters, such as neighbors, family members, ex-girlfriends and bosses. These interactions fueled the show, causing dramatic sequences, and putting the group into hysterical situations that you or someone you know have dealt with before.
With each story, a word or phrase would come about to explain the situation at hand. While you might have your own terms in your friendship circle, here are some Jerry, Elaine, George and Kramer's best Seinfeldian words and phrases with their meanings (via Wikipedia).
Assman: 1) A Proctologist 2) A person who displays his/her name on vanity license plates
Close Talker: One who speaks to a person at point blank range (usually with both peoples' noses less than a foot away from the other)
Festivus: A made up holiday
Get Out!: What a woman might say to her friends in complete surprise (while at the same time shoving them backwards)
Head-First Parker:A person who tries to pull into a parking space head first as opposed to backing into the space, possibly with the intention of screwing someone else out of the space
Jerk Store: A phrase that is used as part of a put-down by a naive person who can't think of any better put-downs to use
Key Brothers: Friends who exchange each others' apartment or house keys, with the provisional that they follow the key covenant
Little Kicks: A horrendous dance performed by a seemingly attractive woman, in which she completely turns off coworkers and friends alike
Manzire: A bra created for older men who have excess flab in the upper chest area and give the appearance of having breasts
Mulva: What to call your current girlfriend if you can't remember her name
Pre-Emptive Break-Up: When a man anticipates that his girlfriend is going to break up with him, so he breaks up with her first (so that he can have hand)
The Puffy Shirt: 1) A funny looking white shirt with ruffles in the front, and puffy looking long sleeves, similar to what pirates would wear 2) What to wear when being a guest on a TV talk show
Shrinkage: 1) What happens to a man's genitalia after being in contact with water (especially cold water) 2) What to tell a woman who mistakenly sees a man's genitalia in the shrunken stage, and finds it humorous
Spare A Square: What to ask a person if one happens to be in a public bathroom stall and runs out of toilet paper
Vandelay Industries: 1) A fictitious company which manufactures latex 2) A company which is made up by someone who is out of work and is trying to convince the Department of Unemployment that he/she is being considered for a job with the fictitious company to keep up his/her unemployment benefits
Yada, Yada, Yada: What a person might say, mid-sentence, to shorten a story to get to the point of a discussion or to hide any incriminating activities