3 sentences for 凹 (āo — concave)

1. 木板上有一道用来固定的凹槽。

   mù​bǎn shàng yǒu yī dào yòng​lái gù​dìng de āo cáo.

   There is a groove in the wooden board for fixing it in place.

   Source: Dong Chinese Dictionary

2. 这种地板通过凹凸的沟槽进行拼接。

   zhè zhǒng dì​bǎn tōng​guò āo tū de gōu cáo jìn​xíng pīn​jiē.

   This flooring is joined using tongue and groove joints.

   Source: Dong Chinese Dictionary

3. 这块金属板被撞了一次，中间凹下去了一块。

   zhè kuài jīn​shǔ​bǎn bèi zhuàng le yī cì, zhōng​jiān āo xià​qù le yī kuài.

   The metal plate was hit once, and a section in the middle got dented.

   Source: Dong Chinese Dictionary