Slacklining is a balance sport that uses nylon webbing tensioned between two anchor points. Slacklining is distinct from tightrope walking in that the line is not held rigidly taut. (Source: Wikipedia)
Slacklining can be traced back to climbing camps in Yosemite during the mid 1970s. Climbers would camp there for weeks blazing new routes up the mountains and in their time on the ground they starting rigging lines to walk across. The line's tension can be adjusted to suit the user and different types of dynamic webbing can be used to achieve a variety of feats.
Styles of slacklining include tricklining that is done low to the ground, waterlining or slacklining over water, highlining or slacklining at large distances above the ground or water, and so on.