Boston English pronunciation of chowder. This invariably refers to New England clam chowder, a thickish, creamy soup made mostly from clams and potatoes. There's no definite standard for the spelling - you will see "chowda" and "chowdah" in equal numbers written in chalk under "Soup of the Day" in any down-homey seafood restaurant in New England. In fact there is a chain of restaurants called "The Boston Chowda Company", which sells soup, mostly (you guessed it) New England Clam Chowder.
This pronunciation is one of the canonical examples of Boston English, and is considered important because it differentiates New England clam chowder from others, such as Manhattan Clam Chowder, which is tomato-based. So deep is the rivalry between Boston and New York City that it is illegal to make Manhattan Clam Chowder in Massachusetts, owing to a little-known law which makes the use of tomatoes in the production of clam chowder illegal.
The power of this word is demonstrated no better than on an episode of The Simpsons called The Boy Who Knew Too Much, where Freddy Quimby (nephew of "Diamond" Joe Quimby and obvious parody of one of the Kennedy boys) administers a savage beating to a foreign waiter over the pronunciation of "chowder":
Freddy: Hey! What the hell is this?
Waiter: [French accent] It's a bowl of chowder, sir. [he pronounces it "shau·dair"]
Freddy: Wait a minute, come here. What did you call it? Say it loud enough so everyone can hear. Come on, say it...
Waiter: Ahem. Chowder. ["shaudair" again]
Freddy: [raucous laughter] Shau-dere? Shau-dere? It's "chowder". ["chowdah"] Say it right!
Waiter: [pause] Chowder. ["shaudear"]
Freddy: [laugher] Come back here! I'm not through demeaning you.