What is Swing?
"Swing" is a hard term to define, as it expresses a personal interpretation of rhythm based mostly on 'feeling'. Therefore, to fully understand what swing means, we encourage you to listen to a lot of music that has a swing feeling to it in order to grasp the different interpretation that various musicians have of swing rhythms.
When music is not played swing, it is referred to as straight. Some musicians are said to have a harder swing than others, meaning that their interpretations are farther from a straight version of a piece than others.
To illustrate what a swing rhythm may sound like, try to play a short series of 8th notes straight, but play the last note slightly too late. There you go, you are already 'swinging'!
Note: EarMaster's Jazz course includes hundreds of rhythm live tapping exercises with Swing.