Louis Armstrong described swing this way, "Ah, swing. Well, we used to call it ragtime, then blues – then JaZz. Now, it's swing. White folks, y'all sho is a mess. Swing!"
I recall a few years ago doing a gig with an accompanist who was not a JaZz cat. I pulled out some charts and introduced him to a few tunes. Upon reviewing the chart for a swing tune, the pianist exclaimed, "Oh, a bouncy tune!" That was certainly an interesting manner in which to describe swing, but not necessarily inaccurate.
Let's see if I can clarify this a little ... at least as clear as mud, anyway. (LOL) Swing has nothing to do with time, as you can swing to any tempo. It does have everything to do with rhythm. Swing has a strong rhythmic groove; meaning a propulsive feel or a type of rhythmic patterning.
Ask just about any experienced JaZz musician to define it and while some may feel hard pressed to come up with the words, you can be guaranteed that they are intimate with the feel. According to Wikipedia, "as a performance technique, swing has been called 'the most debated word in JaZz.' When JaZz [trumpeter] Cootie Williams was asked to define it, he joked, 'Define it? I'd rather tackle Einstein's theory!'"
The "JaZz in America" glossary defines it as "... when an individual player or ensemble performs in such a rhythmically coordinated way as to command a visceral response from the listener (to cause feet to tap and heads to nod); an irresistible gravitational buoyancy that defies mere verbal definition."
Now that's a mouthful! Suffice it to say that you'll know it when you feel it. And while I could continue to ramble on, let me instead direct you to two of the finest performers in the history of JaZz who are the incontrovertible epitome of swing: Ella Fitzgerald and Duke Ellington. Now those cats could swing!
Hugs, Carolena