To begin with, Swing is Music. Some people consider swing to be a kind of a dance, defined by steps. They will dance (and even teach) this dance to all sorts of music, including Rock'N'Roll, Disco, C&W, etc. They don't think of Swing as African-American or as Jazz ... they tend to think that swing started in the 50's or 40's ...
What is Swing music? Swing music is a kind of Jazz music. It has African roots and European roots. The classic swing dance bands were Chick Webb, Count Basie, Jimmie Lunceford, Cab Calloway, Duke Ellington, Fats Waller. Louis Armstrong, ... Swing music does not have a hard beat. It has a strong flow. Swing dancing is jazz dancing. You play. You improvise. You syncopate. Rock (&Roll), Rockabilly, and various other musical forms evolved from Swing music. Swing music started in the mid-1920's, and was really popular among African Americans until it entered the mainstream around 1935. It was wildly popular until about 1945, when people danced much less, and Jazz, which had always been dancing music, stopped being popular. R&B and Jump Blues, which had grown out of Swing, combined with C&W and gave rise to Rock & Roll. This too was started by African Americans. R'N'R eventually grew into Rock, and became completely undanceable. In the 1970's there was Disco, and later C&W and Rockabilly.
In the 1980's, several people rediscovered authentic Swing music and dancing, inspired by the Lindy Hop in such films as Hellzapoppin' and Day at the Races. This lead to a resurgence of real Swing music, as thousands of people learned to dance Lindy Hop from the old masters like Frankie Manning and Al Minns, and the new masters, like Steven Mitchell and Ryan Francois. The film Swing Kids, which contains Swing music and dancing, was choreographed by Ryan Francois.
At the same time, in the 1980's several Rock, Rockabilly, Ska, and Punk bands were inspired by the popularity of Swing, to call themselves Swing bands. This music is often called Neoswing. It sounds and feels a lot more like Rock than Swing, often with a hard beat, and an angry edge. BBVD, CPD, BSO, and JFO are Neoswing bands. SNZ are inspired by pre-swing music - ragtime and hot jazz.
And then there are many, many contemporary authentic swing bands -- Bill Elliott, Eddie Reed, Dean Mora, Jennie Loebel, Lavay Smith, Joe Salzano, Lindy Hop Heaven. Swing music is pure joy. It puts a smile on your face. Toronto now has several excellent swing jazz dance bands. They can be heard at places such as the Reservoir Lounge. And people danced to their music at such places as Gypsy Co-op and for five months in 1999, at the historic Palais Royale Ballroom.
Swing is Jazz music - Jazz is Dancing music - Swing music is Pure Joy.