Ūṣmapa (Ushmapa) is one kind of Pitṛgaṇa (Pitrigana; Forefathers’ spirits). The Ūṣmapa forefathers have a special characteristic feature, that they drink hot liquid. Though the term itself carries the sense of drinking, in the commentary of Bhagavadgītā (Bhagavadgita), citing the sources of Śruti (Sruti) and Smṛti (Smriti), Śrīdharasvāmi (Sridharaswami) has said that this kind of Pitṛgaṇa are the partakers of the ‘ūṣma’ (ushma; hot) elements of a yajña (yajna)–
ūṣmabhāgā hi pitaraḥ ityādiśruteḥ.
But in the Smṛti-pramāṇa (Smritipramana; proof or evidence collected from the Smriti-texts), it is said that the ūṣmapa Pitṛgaṇa can consume the rice offered in śrāddha(sraddha)-ritual, as long as the rice offered in śrāddha remains hot, and the one who performs the śrāddha, continues to sing the praise of hot ghee —
yāvaduṣṇaṁ bhavedannaṁ yāvadaśnanti vāgyatāḥ
pitarastāvadaśnanti yāvannokto havirguṇaḥ.
Ūṣmapa is one of the Pitṛgaṇa who used to stay in the sabhā (sabha; court or assembley) of Yamarāja(Yamaraja), and worshipped him.