Attention, class is in session...lol
back to the Grove Dictionary of Music & Musicians:
In Western notation the group of sharp or flat signs placed at the beginning of a composition, immediately after the clef, or in the course of a composition generally after a double bar. The signs affect all notes of the same names as the degrees on which they stand, and thus define the key of the composition.
Western notation basically refers to notation on basic 5 line staff.