Upādāna: 'clinging', according to Vis.M XVII, is an intensified degree of craving tanhā. The 4 kinds of clinging are: sense-clinging kāmupādāna, clinging to views ditthupādāna clinging to mere rules and ritual sīlabbatupādāna, clinging to the personality-belief atta-vādupādāna.
1;What now is the sense-clinging? Whatever with regard to sense-objects there exists of sense-lust, sense-desire, sense-attachment, sense-passion, sense-confusedness, sense-mental chains: this is called sense-clinging.
2 What is the clinging to views? 'Food and offerings are useless; there is no fruit and result for good and bad deeds: all such view and wrong conceptions are called the clinging to views.
3;What is the clinging to mere rules and ritual? The holding firmly to the view that through mere rules and ritual one may reach purification: this is called the clinging to mere rules and ritual.
4;What is the clinging to the personality-belief? The 20 kinds of ego-views with regard to the groups of existence see: sakkāya-ditthi these are called the clinging to the personality-belief; Dhs. 1214-17.
This traditional fourfold division of clinging is not quite satisfactory. Besides kamupādāna we should expect either rūpupādāna and arūpupādāna or simply bhavupādāna Though the Anāgāmī is entirely free from the traditional 4 kinds of upādāna he is not freed from rebirth, as he still possesses bhavupādāna The Com. to Vis.M XVII, in trying to get out of this dilemma, explains kāmupādāna as including here all the remaining kinds of clinging.
Clinging' is the common rendering for u., though 'grasping' would come closer to the literal meaning of it, which is 'uptake'; see: Three Cardinal Discourses WHEEL 17, p.19.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.