Receptor adaptation is the diminishing of response to a constant stimulus. Some receptors do this completely (stop responding) and are called phasic, while others will continue to respond for the duration of the stimulus and are referred to as tonic. Given this, phasic receptors allow our nervous systems to ignore stimuli that are not critical to function, saving processing abilities for more essential inputs. Of note, phasic and tonic does not refer to the speed with which the receptor adapts (partially or completely). There are both fast and slow phasic and tonic receptors.
