Vyapti in Indian Logic refers to:

Vyapti names the invariable, universal concomitance between the reason (hetu) and the thing to be proved (sadhya).

It holds that wherever the mark is present the target property is always present too, as smoke is everywhere accompanied by fire.

This pervasion is the logical backbone of inference (anumana) in Nyaya.

Only when such a fixed relation is grasped can the mind move validly from sign to conclusion.

It is thus a relation of constant accompaniment, quite distinct from perception or verbal testimony.