A push happens when the result hits a whole-number line exactly: under 3.0 goals with the match at 3, a -3 spread won by 3. The stake returns; the bet is a non-event. Asian handicaps use the same mechanic on their whole and half-split lines.
Two practical consequences: pushed bets do not count toward bonus wagering at most books, and in accumulators a pushed leg usually drops out — the coupon recalculates at the remaining odds rather than dying.
Over 2.5/3.0 (a split Asian total) with the match ending 3–0: the 2.5 half wins, the 3.0 half pushes — you collect on half the stake and get the other half back. On a plain over 3.0, the whole stake would simply return.