In sports betting, the term "1" typically refers to a betting odds format known as "Home Win" or "Team 1 to Win." It means that you are placing a bet on the outcome where the home team wins the event or match.
1/1 is an Half-time/Full-time betting market. It means the Home team is going to win at halftime and Fulltime. In other words, to win a 1/1 bet; By the end of the first half, the home team should be winning. By the end of the whole match (full-time), the home should be the winner.