Prathama-prakaraṇam (Yama) · Verse 55
कर्मणा मनसा वाचा सर्वावस्थासु सर्वदा । सर्वत्र मैथुनत्यगो ब्रह्मचर्यं प्रचक्षते ॥
karmaṇā manasā vācā sarvāvasthāsu sarvadā | sarvatra maithunatyago brahmacaryaṃ pracakṣate ||
Brahmacarya is defined as maithunatyaga — renunciation of sexual activity — in action, mind, and speech, at all times, in all states, everywhere. This is the most comprehensive definition possible, leaving no loophole. The triple domain — karmaṇā manasā vācā — means that even mental and verbal sexual engagement violates brahmacarya. This strict definition applies particularly to the renunciate path.