(I've been swing dancing 13 years, playing swing music for 6) This article is very thorough and gets across the nuance and futility of trying to define "swing"

(I've been swing dancing 13 years, playing swing music for 6) This article is very thorough and gets across the nuance and futility of trying to define "swing" with only a few rules. See especially the section on swung eighth notes: > Swung-eighths. This is where it gets cool and tricky, and if you want to swing like crazy, you have to understand this one. When you swing the eighth notes, it means that you take a triplet, and you skip the middle sound. Essentially what you end up with is 1 and a 2 and a 3 and a 4 and a [side note, as a way to emphasize the beginning of the phrase, you’ll sometimes hear 1 2 a3 4 a5 6 a7 8 a]. This rhythm is common in Gypsy Jazz or Jazz Manouche and is sometimes referred to as a shuffle. This, you may note is a 2:1 ratio. Much swing music is actually played closer to a 3:2 ratio, which is less displaced, but again there isn’t a great way to notate this, so it’s more understood than proscribed. (The original has strikethrough formatting which has been lost in copy/paste) To make it even more confusing, often rhythm players (guitar, drums, etc) will keep the swing ratio consistent (across a song, or across a phrase) whereas melody players (trumpet, sax, etc) might play with the ratio within a melodic phrase. Another thing that makes swing swing is syncopation — the author alludes to this but doesn't define it — namely placing emphasis on the swung eighth notes that lie between quarter notes, rather than on one of the quarter note beats. Straight vs swung, and syncopated vs non-syncopated can exist independently, and you need swung and syncopated for it to feel like swing.