Beauty here means that appeals to one's mind and attracts it and produces an intent of being close to the thing having this attribute. This attribute of things is probed here from human point of view but may be applicable to other species also.
From classical point of view, we sense five attributes - view, sound, smell, taste and softness, of things through our five sensory organs - eyes, ears, nose, tongue and skin. I add here the sixth attribute of 'concept' sensed by our 'perceptibility'. To clarify about this sixth attribute, I would like to mention that very often we appreciate a thought expressed in words, or even selection of words expressing a thought. This is also a beauty and is not included in the five attributes mentioned in classical literature. Finally, based on the six attributes, our minds judge whether the thing is beautiful or not.
Whenever, some thing beautiful comes to our mind, we make a mental image of it and we see or feel the thing, we compare it with our mental image. The thing may appear better, similar or worse than our mental image. Accordingly, we rate the thing 'extremely beautiful', 'beautiful', or 'not-so-beautiful' etc. This is the basis of a familiar concept about beauty that it lies in the eyes of the beholder.
This concept is highly subjective and serves only a limited purpose of inter-relationships. At some time later, I shall probe what is beauty from objective angle.