Charge-canceling is the act of canceling or storing a charged neutral special move, such as Samus' Charge Shot.
While charging such an attack, players can shield to cancel/store the charge, or tap left/right on the control stick or d-pad to immediately roll out of the charge, which also cancels/stores it.
Some charge attacks can be charged and canceled in the air, such as Donkey Kong's or Sheik's. To cancel a charge in the air, players can simply press Z while charging.