Agility is a skill that can aid adventures in getting around runescape.  Increasing your level in agility will decrease the rate that your run energy drains and increase the rate at which it restores when not running.  Certain agility levels are required to pass obstacles in order to get to otherwise unreachable areas, and access shortcuts.  You can train agility by using the various agility courses throughout runescape.  As of December 05 2013, players may also train agility using rooftop agility courses.