In philosophy the term refers to individual instances of subjective, conscious experience. For example, two people looking at the same rose describe its color as RED. However, what each experiences may be very different. What one defines as RED the other may define as orange or even blue. This would apply equally to any of the senses.
This type of research is generally less quantifiable and does not require statistical accuracy. Emphasis is placed on "quality of information" gathered such as consumer perceptions and attitudes.