Supra-aural headsets have earpads that rest on the ears, but not around them. Circumaural headsets have earpads that completely envelop, or cup, the ears.
Supra-aural headsets are usually smaller and more lightweight, and therefore more portable. However, while supra-aural headsets are generally better at noise canceling than headsets that use earbuds, they are not as effective as circumaural headsets. Circumaural headsets are larger and heavier because the earpads are constructed of higher-density foam, so the fact that the ears are completely enclosed results in better noise canceling effects for the user.
Circumaural headsets are ideal for in high noise environments where sound clarity is essential, such as military, aviation and industrial environments.