to become slightly sweaty; to begin to perspire lightly so that skin or clothing becomes a bit damp.
夏の朝、外を少し歩いただけで背中が汗ばんだ。
On a summer morning, just walking a bit outside made my back slightly sweaty.
緊張して手のひらが汗ばむ。
When I'm nervous, my palms get slightly sweaty.
部屋の湿度が高くて首筋が汗ばんでいる。
The room's humidity is high and the back of my neck is damp with sweat.
長時間座っていると、椅子に腰が汗ばむことがある。
Sitting for a long time sometimes makes the lower back area damp with sweat on the chair.