Aesthetic appreciation refers to the sensory appraisal of objects using the normative system of aesthetics, which judges the quality of objects based on how pleasing they are to the sense. Aesthetics at large is the branch of philosophy concerned with the nature of taste, art and beauty.
Aesthetics as a philosophical branch encompasses a number of different normative systems. As tastes vary from person to person, the notion of varied tastes applies on a systemic level to aesthetics where various philosophers have articulated their notion of what makes an object appealing or unappealing to the senses. These notions vary wildly, so there is no consistently accepted metric for judging objects based on their pleasantness.
By the nature of the term, aesthetic appreciation can involve the use of any of these metrics and does not require a certain conclusion by an individual. Rather, any decision about how pleasant an object is to the senses that can be defended by an aesthetic theory articulated by a recognized philosopher would be a form of aesthetic appreciation.
The idea of aesthetics itself emerged in the 18th century. Beyond making judgments of qualities, aesthetics is also used to organize objects into groupings called genres.