输 (shū) is a verb meaning "to lose" in the context of a competition, game, or contest. It is the opposite of 赢 (yíng, to win). For example, 总是输 means "always loses."
这场比赛我们输了,下次再努力吧。
zhè chǎng bǐsài wǒmen shū le, xià cì zài nǔlì ba.
We lost this match; let's try harder next time.
他下棋从来不输,大家都很佩服他。
tā xiàqí cónglái bù shū, dàjiā dōu hěn pèifú tā.
He never loses at chess; everyone admires him.
别怕输,重要的是参与。
bié pà shū, zhòngyào de shì cānyù.
Don't be afraid of losing; what matters is participating.