The part of you that watches.
In Patañjali's Yoga Sūtra, the draṣṭā is the seer: the one who watches thought and feeling without being carried off by them. Drishta takes its name from that word.
Most of us are never given the time, or the language, to observe our own inner world. We react first and understand later, if at all. Our work is to make that observing a skill you can practise.