If the spread is set at +7, the underdog must either win the game outright or lose by fewer than seven points in order to cover. For the favorite to cover, they must win by more than seven points.
A spread of +7.5 means that the team must either win the game or lose by 7 or less points/goals/runs for the spread bet to win. A spread bet is a bet on the margin of victory with a handicap (or line) attached to it, in this case the handicap is +7.5.