Underwear or undergarments: clothes worn next to the skin (undershirts, underwear, bras, etc.).
新しい下着を買った。
I bought new underwear.
下着は肌に合う素材を選ぶと快適だ。
It's comfortable to choose underwear made of material that suits your skin.
旅行のときは下着を多めに持って行ったほうがいい。
When traveling, it's better to bring extra underwear.