Not knowing or admittedly not being capable of proving or disproving the existence of a superior being or beings.
Either used to show a person as "sitting on the fence" or somebody who is certain that the existence of a supernatural being can't be proven or disproven.
Agnosticism is merely the "ism" for "Agnostic".
Agnostic: In THIS universe everything appears to have a cause. What if something outside of this universe, where the same boundaries don't apply, happened to have an input to the development of ours, perhaps even being as minute as starting a large explosion? Could we call this influence "God" or could we call it Science? Can we even prove anything like this happened? It appears my Agnosticism has deleted the boundaries for common religious arguing.