Śraddhā-Trayā-Vibhāga Yoga · Verse 25
सद्भावे साधुभावे च सदित्येतत्प्रयुज्यते | प्रशस्ते कर्मणि तथा सच्छब्दः पार्थ युज्यते
sad-bhāve sādhu-bhāve ca sad ity etat prayujyate | praśaste karmaṇi tathā sat-śabdaḥ pārtha yujyate
In Being, in good being, ‘Sat’ is used. Also the word ‘Sat’ is used regarding auspicious action, oh Pārtha.
The use of sat. Sat-bhāve — in the nature of Being, in real existence. Sādhu-bhāve — in virtuous/good being. Praśaste karmaṇi — in auspicious, correct action.
Sat means real, true, good, auspicious. It is the principle of existence and rectitude. Everything aligned with truth is sat.