质 (zhì) means 'quality,' 'substance,' or 'nature' and refers to the inherent character or material composition of something. It frequently appears in compound words like 质量 (quality/mass) and 物质 (matter/substance).
这家店的产品质量一直很好。
Zhè jiā diàn de chǎnpǐn zhìliàng yīzhí hěn hǎo.
The product quality of this store has always been very good.
水是一种很常见的物质。
Shuǐ shì yī zhǒng hěn chángjiàn de wùzhì.
Water is a very common substance.
我们要注重教育的质,而不仅仅是量。
Wǒmen yào zhùzhòng jiàoyù de zhì, ér bù jǐnjǐn shì liàng.
We should focus on the quality of education, not just the quantity.