Learn Swedish: Hela kräftskivan sjunger snapsvisan. - The whole crayfish party is singing the drinking song.

This is the main exception of this lesson! Usually, a definite noun modified by an adjective requires the freestanding definite article (den/det/de), such as in den stora kräftskivan (the big crayfish party). However, hela (the whole) and halva (half the) are anomalies: they skip the freestanding article and are placed directly in front of the definite noun.

Does skiva in kräftskivan literally mean "party"?

In modern everyday Swedish, en skiva usually means a "slice" (like a slice of bread) or a "disc" (like a vinyl record). Historically, however, it also meant a feast or party set around a large table. Today, that "party" meaning survives almost exclusively in traditional compound words like kräftskiva (crayfish party) and studentskiva (graduation party).

What is the difference between en visa (as in snapsvisan) and en sång?

Both mean "song", but en visa specifically refers to a traditional, acoustic, or folk-style song. A snapsvisa is a short, lively drinking song sung right before taking a shot. En sång is the broader, general word for any kind of song, including modern pop music.

If I want to say "the whole of the crayfish party", why is there no word for "of" here?