A slight difference; a narrow margin (small gap between two quantities or results).
試合は小差で相手に敗れた。
The match was lost to the opponent by a narrow margin.
世論調査ではその候補者が小差でリードしている。
In the opinion poll, that candidate is leading by a small margin.
点数の小差が勝敗を分けた。
The small difference in points decided the outcome.