One kind of Yajña (Yajna; a holy fire-ritual). This Yajña (Yajna) is created at the beginning of creation from the right -hand face, in other opinion, from the eastern face of Brahmā (Brahma).
Ukthya (The Vedic reading is with ‘ya’ ) is one of the seven kinds of the ancient Jyotiṣtoma (Jyotistama) yāga (yaga) . Ukthya yāga (yaga) is the deformed manifestation of the Agniṣtoma (Agnistoma) yāga (yaga). In the Ukthya yāga (yaga), the three associates of the hotā (hota; the performer of the yajña), read the extra three śāstra (sastra or scriptures) in the third Savana (the process of gifting) after the completion of the reading of twelve śāstras (sastras) in the three Savanas. Therefore, there are fifteen śāstras (sastra) and hence, fifteen stotra or hymns in the Ukthya Yāga (yaga). In this Yāga (yaga), two animals are gifted, one goat to the Agni or fire, and another goat was given as offering both to Agni and Indra (the king of heaven).[Ramendrasundar Rachansamagra, second volume, page-56; H.W. Bodewitz, The Jyotistoma Ritual: Jaminiya Brahmana, I pp.101-107].
Ukthya yāga (yaga) was not very clearly mentioned in Mahābhārata (Mahabharata), but Saptasaṁasthā (Saptasamastha) Somyaga was mentioned in the famous yajña of king Aṅga (Anga). We know that Ukyhya is one of the kinds of the Saptasṁsthā Somyaga (Saptasamstha Somyaga). Ukthya as a kind of famous yāga was marked as part of Agniṣṭoma (Agnishtoma) when Agniṣṭoma yajña was mentioned with the Atirātra (Atiratra), Cāturmāṣya (Chaturmasya) (kinds of yajñas) while narrating the yajña of Yayāti (King Yayati) in the Droṇaparva. Rather Ukthya yāga is more clearly mentioned in Rāmāyaṇa (Ramayana) . According to the Kalpasūtra (Kalpasutra), in narrating the Aśvamedha Yajña (Asvamedha Yajna), Agnistoma on the first day of Aśvamedha (Aswamedha), Ukthya Savana on the second day, Atirātra (Atiratra) on the third day, the number sequence is maintained in this way. This is clear from these thoughts that the performance of yajña (yajna) was not reduced during the periods of Rāmāyana (Ramayana) and Mahābhārata (Mahabharata) and a Vaidika yāga (yaga) without the Veda, Ukthya was highly appreciated.