Fartlek
 n.— «There is a recognised type of running training termed “Fartlek.” Literally translated it means speed play. This is where you have bursts of speed while you are running, with no set pattern, just as the whim to go fast comes to you.» —“Weird Science” by Jane Worthington Sunday Telegraph (Sydney, Australia) Dec. 5, 2004. (source: Double-Tongued Dictionary)