For example, traditional jazz music is written in 4/4
but played in 12/8. Such music may be annotated "with a swing" or similar, but the swing also may be assumed.
Shuffle notation in straight eighths - Shuffle triplet-like performance play
In shuffle rhythm, the first note in the pair is exactly twice the duration of the second note. In swing the division is inexact, and varies depending on factors such as how fast or slow the music is, on the genre of music, or the individual tastes of the performer, from almost equal (typically at fast tempos) to almost shuffle (typically at slow tempos)
http://en.wikipedia.org/wiki/Swing_(jazz_performance_style)