1Sweat; perspiration produced by the body (liquid released from the skin due to heat, exercise, or nervousness).
暑くて汗が止まらない。
It's so hot I can't stop sweating.
運動すると大量の汗をかく。
When I exercise I sweat a lot.
緊張すると手に汗をかく。
My palms get sweaty when I'm nervous.
シャツに汗のシミができた。
A sweat stain formed on my shirt.
2Moisture; condensation that appears on surfaces (not necessarily bodily sweat, but similar moisture/condensation).
朝、窓に汗がついていた。
In the morning there was condensation on the window.
冷蔵庫から出した果物に汗がにじんでいる。
There is moisture on the fruit taken out of the fridge.
3Internet slang interjection expressing awkwardness, embarrassment, or a sheepish 'oops' — often written as '(汗)'.
遅れてすみません…（汗）
Sorry I'm late... (awkward/embarrassed).
会議の資料を忘れた…（汗）
I forgot the meeting materials... (oops).