Charley horse: Slang for a cramp in a muscle in the leg, usually caused by a strain or injury. A charley horse can last anywhere from a few seconds to over a quarter of an hour. It is not uncommon for one to recur before it finally resolves. SLIDESHOW Pictures of the 7 Riskiest Workout Moves, and How to Improve Them See Slideshow From Pain and Injury Resources Painkillers and Opioid Use DisorderPain Relief From Head to Toe Featured Centers What Are the Best PsA Treatments for You?Understanding Biologics 10 Things People With Depression Wish You Knew Health Solutions From Our Sponsors Shot-Free MS Treatment Your Child and COVID-19