Perception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information coming from body receptors and sensory organs into CNS.
Perception involves the entire sensory system from the periphery (sensory receptors) to the higher processing centers in the brain (for example the somatosensory cortex for touch, or the visual cortices for vision). Perception is subjective and may therefore be different from person to person. This tag is therefore suited for questions pertaining the subjective experience of physical stimuli, such as the perception of color, the perception of depth, or the perceptual differences between various odors.
The perception tag refers to processes higher up in sensory systems than sensation. The sensation tag pertains to lower-level processes, such as the peripheral collection of inputs and their processing through earlier stages of processing, e.g. in the thalamus. The perception tag is better suited for the subjective awareness of physical stimuli.
The perception tag is less suitable for questions on sensory receptors per se. For example, physiological questions on the molecular differences between various photoreceptor classes, or the mechanism of action of mechanoreceptors in the ear could better be tagged with the neurophysiology tag, or others.
The perception tag relates to that field of Biology where it meets and overlaps with Psychology. If questions are aimed at the emotional consequences of perception, or target otherwise higher-level cognitive areas such as intelligence or psychological states such as depression or psychosis, consider posting the question on CognitiveSciences.SE. Both Biology.SE and CognitiveSciences.SE consider Neurobiology on-topic, but when questions lean too much toward one side of the Biology - Cognitive Sciences spectrum, questions may face closure when posted on the other side.