Swing dancing began in the 20's with jazz music. It was at it's height of popularity during the 1930's and 40's. In International competitive dance, it is called Jive, a faster beat, and in the American Rhythm competition it is slower and called East Coast Swing.
After WWll many of the big ballrooms were torn down and dancing moved into night clubs. Dance floors were smaller and there wasn't room for swing, so West Coast Swing was invented. West Coast is danced on a straight line, called a slot, thereby taking up very little space. West Coast Swing became very popular and there are clubs all over the US where only WCS is danced.
It's a fun social dance that is usually danced to a blues rhythm. For a couple starting out with social dance, I would highly recommend WCS lessons.