Upadhi: 'substratum of existence'. In the Com. there are enumerated 4 kinds: the 5 groups khandha, sense-desire kāma mental defilements kilesa,, kamma. In the suttas it occurs frequently in Sn. vv. 33, 364, 546, 728, and, with reference to Nibbana, in the phrase;the abandoning of all substrata.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.