胃 (wèi) means "stomach." It refers to the digestive organ and is used in medical, everyday, and figurative contexts. It also appears in compounds like 胃口 (appetite).
我最近胃不太舒服。
Wǒ zuìjìn wèi bú tài shūfu.
My stomach hasn't been feeling well lately.
他吃太多辣的东西,伤了胃。
tā chī tài duō là de dōngxi, shāng le wèi.
He ate too much spicy food and hurt his stomach.
早上空腹喝咖啡对胃不好。
zǎoshang kōngfù hē kāfēi duì wèi bù hǎo.
Drinking coffee on an empty stomach in the morning is bad for the stomach.