slacklining

Etymology

slackline + -ing.

noun

1. A sport resembling tightrope walking but with the rope or webbing only partially taut.
   Highlining was a high-wire version of slacklining, an extreme cousin of tightrope walking in which no pole was used for balance and the rope was elastic, allowing for various tricks involving walking, sitting, lying down, flipping, even spinning hula hoops. March 14, 2008, Jeré Longman, “900 Feet Up With Nowhere to Go but Down”, in New York Times

verb

1. present participle and gerund of slackline