Reserved or modest in behavior or expression — restrained, low-key; can also mean moderate or not excessive in amount or degree.
彼女は控えめな性格で、いつも落ち着いている。
She has a reserved personality and is always calm.
今年のボーナスは控えめな金額だった。
This year's bonus was a modest amount.
派手に目立つより控えめな服装が好きだ。
I prefer modest clothing to flashy, attention-grabbing styles.