清淡 (qīngdàn) is an adjective meaning "light" or "mild" when describing flavor. It is used to talk about food that is not heavily seasoned, greasy, or spicy. For example, 味道清淡 means "the flavor is light."
医生建议我最近饮食要清淡一些。
yīshēng jiànyì wǒ zuìjìn yǐnshí yào qīngdàn yìxiē.
The doctor recommended that I eat lighter food recently.
这道汤味道很清淡,适合老人喝。
zhè dào tāng wèidào hěn qīngdàn, shìhé lǎorén hē.
This soup has a light flavor, suitable for elderly people to drink.
我今天胃不舒服,想吃点清淡的。
wǒ jīntiān wèi bù shūfu, xiǎng chī diǎn qīngdàn de.
My stomach is upset today, I want to eat something light.