Outbound or outward bound has its origins in sailing where it stands for the moment the ship leaves its harbour towards the open seas which hold unknown adventures. An outbound programme uses the outdoors as a classroom with the rivers, rocks and trees - in short, Mother Nature as training material.
Experiential means the person learns and understands various aspects of his/her personality through his/her experience in various activities, mind games and exercises.
Learning through such personal experience is powerful and remains with people for long years to come.