The noun 垫子 (diànzi) means "cushion," "mat," or "pad." It refers to a soft object placed on a surface for comfort or protection. For example, 椅子的垫子下面 means "under the chair cushion."
沙发上的垫子很软,坐着特别舒服。
Shāfā shàng de diànzi hěn ruǎn, zuò zhe tèbié shūfú.
The cushion on the sofa is very soft; it's especially comfortable to sit on.
你把那个垫子放在地上,我们可以坐在上面。
Nǐ bǎ nàge diànzi fàng zài dìshàng, wǒmen kěyǐ zuò zài shàngmiàn.
Put that cushion on the ground and we can sit on it.
瑜伽垫子忘在健身房了,明天去拿。
Yújiā diànzi wàng zài jiànshēnfáng le, míngtiān qù ná.
I left my yoga mat at the gym; I'll go get it tomorrow.