तत्सदिति निर्देशो ब्रह्मणस्त्रिविधः स्मृतः।ब्राह्मणास्तेन वेदाश्च यज्ञाश्च विहिताः पुरा
oṁ tat sad iti nirdeśho brahmaṇas tri-vidhaḥ smṛitaḥ brāhmaṇās tena vedāśh cha yajñāśh cha vihitāḥ purā
Om Tat Sat is the triple designation of the Eternal Spirit, by which the Vedic Scriptures, ceremonials, and sacrifices were ordained of old.
Translated by Shri Purohit Swami
"Om Tat Sat": This has been declared to be the triple designation of Brahman. By that, the Brahmanas, the Vedas, and the sacrifices were created formerly.
Translated by Swami Sivananda
Word meanings (from the gita/gita dataset)
om tat sat—syllables representing aspects of transcendence; iti—thus; nirdeśhaḥ—symbolic representatives; brahmaṇaḥ—the Supreme Absolute Truth; tri-vidhaḥ—of three kinds; smṛitaḥ—have been declared; brāhmaṇāḥ—the priests; tena—from them; vedāḥ—scriptures; cha—and; yajñāḥ—sacrifice; cha—and; vihitāḥ—came about; purā—from the beginning of creation