It means that if a team who is the handicap favourite wins by two goals or one goal. For example you'd see team A (-1) draw (-1) team B (+1) , team A wins 1-0 or 2-1 by a one goal margin then the -1 draw would come through .
Handicap betting is where one selection in an event is given a "handicap" to overcome in order to win. This is popular when strong favorites are playing, instead of placing a match bet at short odds, you can place a bet at longer odds with a 1 or 2 goal start, or -12 point for instance.