Gotama claimed that our identity is based on one or more of these five. When we understand we are not any or all of these five, then we have attained a high level of development.
The skandhas (Sanskrit) or khandhas (Pāli, aggregates in English)
The Five Aggregates are (with the Pali):
Material form is described by the Four Great Elements: solidity, fluidity, heat and motions. Material things (like everything else) comes in six kinds:
And the corresponding objects of these sense organs: sights, sounds, smells, tastes, touch-feelings, and some thoughts and ideas, These are the whole of the physical world.
Feelings or sensations arise when a sense organ makes contact with its object. Feelings are pleasant, unpleasant or neutral. They are of six kinds, for instance, pleasure on seeing something or disgust on smelling something. Feelings are based on the following:
In Buddhism, Perception is recognition of things. The word perception is not used exactly as it is used in English. It has six kinds:
Volitional Mental Formations are mental actions that direct the mind to good, to bad or to neutral activities. Contrasting with perception and feeling which are not volitional actions and so do not produce karma, mental formations do produce good and bad karma.
Like perception and feeling, they are of six kinds, corresponding to the six sense media − mental phenomenon can appear to have colour, shape, sound, etc.
Mental Formations include:
These are the important twelve of the 52 types listed in the literature.
They are our stored-up karma.
Consciousness is the awareness of something without recognition (perception), or before recognition. So consciousness is aware that something is there, but perception determines what it is. I hear a sound (consciousness) and recognise it is a cat meowing (perception). Like feeling and perception, consciousness comes in six kinds corresponding to the sense media.
Gotama said that the five clinging aggregates (pañcupadanakkandha) are suffering.
Whatever we think we are is based on these five aggregates. We are them and they are us. They bring about our thoughts, feelings, ideas, evaluations and attitudes that filter and create our experience. Gotama said that the five clinging aggregates are suffering. They are suffering because they are impermanent. They change from moment to moment. Because they build and filter our world and because they are suffering, it means, therefore, that our world (but not necessarily the world) is suffering too.
Gotama said he taught subduing craving for these five Skandhas, because when they change or alter, as they inevitably do, there will be no stress and upset. See: SN 22.2
Also see How to Catch a Monkey
Because of this, the Five Skandhas are important in Buddhism.