You talk about afferent signals in the CNS and then mean that the signal is on its way into a particular area. For example, one can speak of the afference of a certain cerebral cortex area or of the afference of the bark area. This refers to the signals that are led into the bark area.
In PNS , the term "afference" refers to signals that are to be submitted to the CNS and the term then includes all signaling from sensory organs of various kinds.
Cf. Efferens