Before revision:  A canalizing update rule is one for which the node state at time t is determined by the state at time t-1 of a particular one of its inputs when that input is in its canalizing state.
After revision:  A canalizing update rule is one for which a node state at time t is determined by the state at time t-1 of a particular one of its inputs when that input is in its canalizing state.