The so-called “aggregate of feeling” is an overall label for feelings. There are essentially three kinds: pleasant, unpleasant, and a neutral feeling which is neither pleasant nor unpleasant.

How are these feelings produced? When the eye perceives matter that is pleasant or unpleasant, this thought is transmitted to the sixth consciousness; our consciousness follows the eye and forms an attachment; desire and anger arise as a result. Anger here implies a lack of acceptance; we do not necessarily get angry at everything that is unpleasant, but when we refuse to accept, try to avert, or bear thoughts of resentment, this is also called anger.

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