Something that's encompassing completely encloses or surrounds something else. An island, for example, sits in the midst of encompassing ocean waves.
The adjective encompassing can describe things that literally encircle something, and also things that are so extensive that they seem to do so. For example, an encompassing history of World War II would include everything about the period, including the Holocaust. Encompassing comes from the verb encompass, "surround and hold within," or "include comprehensively," from the roots en-, "put in," and compass, "space or circumference."