The point spread handicaps the favourite by a margin of victory the team must cover. It is the default NFL and college football market because it levels closely priced matchups — both sides are priced near −110, so the spread itself is the variable.
A line of "Chiefs −6.5 vs Broncos +6.5" means the Chiefs must win by 7 or more for a spread bet on them to cash. The Broncos cover if they win outright or lose by 6 or fewer. Hooks (half-points) eliminate the chance of a push — a spread of −7 can tie at 7, but −6.5 cannot.
When the spread is a whole number (−3, −7, −10) and the favourite wins by exactly that margin, the bet pushes — your stake is refunded. Sportsbooks intentionally avoid the most likely push numbers (3, 7) by setting half-points just above or below.
Most Nebraska books let you buy a half-point of spread for a worse price — moving from −6.5 (−110) to −6 (−130) for a chance to push instead of losing. Worth it on key NFL numbers (3 and 7) but rarely worth it on irrelevant numbers.