An inner act of the heart consisting in formulating one's intention to perform an outer act as the fulfillment of a particular duty (rather than as just a series of motions without religious value). Ritual actions such as the prayer, the pilgrimage, and the ablutions are invalid in the absence of proper intent.
A famous hadith (#1 in al-Nawawi's Forty Hadith) states that "actions are according to intent" (or "actions are what they are by virtue of intent.")