That specific characteristic of the Pudgala (physical substance), on account of which it has the capacity to form aggregate mutually with other Pudgalas as well as to get associated with the Jīva (soul).
poggalatthikāe......guṇao gahaṇaguṇo.
grahanam- parasparena sambandhanamjīvena vā audārikādibhih prakārairiti.
(Bhaga 2.129 Vṛ)