In a nutshell, A "Scouts Own" is an inspirational ceremony, usually built around a central theme, such as friendship, world peace, save the earth, or appreciation of the world around us. Just about any topic consistent with the principles and program goals of Scouting is appropriate. The important thing is that it be the work of the Scouts themselves---from start to finish. Officially, the Boy Scouts of America has discontinued the use of the term “Scouts Own” and replaced it with “interfaith worship service” or “outdoor worship service”.
The First “Scouts Own” ceremonies were introduced in 1909 by “Uncle” H. Geoffrey Elwes, a pioneer in Scouting along side Baden Powell, at the Crystal Palace Rally, the precursor to Scouting’s World Jamborees. They were originally meant to be simple interdenominational religious celebrations.
Baden Powel expanded on the idea and in 1928 described it as;
“For an open Troop, or for Troops in camp, I think the Scouts' Own should be open to all denominations, and carried on in such a manner as to offend none. There should not be any special form, but it should abound in the right spirit, and should be conducted not from any ecclesiastical point of view, but from that of the boy. Everything likely to make an artificial atmosphere should be avoided. We do not want a kind of imposed Church parade, but a voluntary uplifting of their hearts by the boys in thanksgiving for the joys of life, and a desire
on their part to seek inspiration and strength for greater love and service
for others. In execution, a "Scouts Own" can range from lively to somber.
The intent is generally serious, however, and usually reflective. Texts used
can be spontaneously made up or taken from existing literature. If readings
from sacred works (scripture) are incorporated, Scouts should be
encouraged to choose passages that are less likely to offend (such as, not
referring to the Deity by a name identified with a specific religion).
Information referenced from Wikipedia and Language of scouting