Somewhat thin or narrow; used to indicate something is a bit thinner or narrower than usual.
そのズボンは細めのシルエットでかっこよく見える。
Those pants have a somewhat narrow silhouette and look stylish.
ペン先は細めのものが書きやすい。
A thinner pen tip is easier to write with.
帯は細めのものを選ぶと洋服に合わせやすい。
Choosing a narrower belt makes it easier to match clothing.