What does "分母" mean?

各种转发/评论抽奖活动的参与者。把中奖概率看成是分式的话，奖品（分子）有限的情况下，参加抽奖的人（分母）愈多，中奖概率也就越小

ENParticipants in various repost/comment lottery activities. If you think of the winning probability as a fraction, with a limited number of prizes (numerator), the more people who participate in the lottery (denominator), the smaller the winning probability.