Wearing light clothing; being lightly dressed. Also refers to such light clothing.
今日は暖かいから薄着で出かけても大丈夫だろう。
It's warm today, so it should be fine to go out lightly dressed.
薄着で夜風に当たると風邪を引きやすい。
Being lightly dressed and exposed to the night breeze makes it easy to catch a cold.
寒い電車内で薄着の人をよく見かける。
I often see people lightly dressed on cold trains.