In Abhidharmakosa, all composite phenomena are summed up as the five aggregates – form, feeling, perception, volition, and consciousness. The so-called “aggregate” means the coming together of a lot of things.

The aggregate of form denotes not only phenomena perceived by the eye, but also sounds heard by the ear and all kinds of appearances like weight, light, darkness, etc. In other words, the aggregate of form is an overall name for all of the things above.

To facilitate the understanding of these concepts, we shall utilize language that is familiar to everyone. The aggregate of form in Buddhism refers principally to the body and external objects; the aggregates of feeling, perception, volition, and consciousness refer primarily to the mind, and the activities of the body, matter, and mind. The aggregate of form shall first be explained.

- Quote from The Four Seals of Dhama, "The Practice of Realizing Emptiness"