A global symmetry is a symmetry that holds at all points in the spacetime under consideration, as opposed to a local symmetry which varies from point to point.
Global symmetries require conservation laws, but not forces, in physics.
An example of a global symmetry is the action of the (for a constant - making it a global transformation) group on the Dirac Lagrangian:
Under this transformation the wavefunction changes as and and so clearly:
Famous quotes containing the words global and/or symmetry:
“Ours is a brand—new world of allatonceness. “Time” has ceased, “space” has vanished. We now live in a global village ... a simultaneous happening.”
—Marshall McLuhan (1911–1980)
“What makes a regiment of soldiers a more noble object of view than the same mass of mob? Their arms, their dresses, their banners, and the art and artificial symmetry of their position and movements.”
—George Gordon Noel Byron (1788–1824)