Quality or value of something or someone; often used for product quality or level of performance.
このワインは質が高く、香りも豊かだ。
This wine is of high quality and has a rich aroma.
値段だけでなく、製品の質を重視してください。
Please value the product's quality as well as its price.
人材の質が会社の将来を左右する。
The quality of personnel determines the company's future.
The nature or inherent character of something; its essential traits (similar to 'nature' or 'character').
この問題の質をよく理解することが重要だ。
It's important to fully understand the nature of this problem.
彼の話し方から、その人の質が伝わってくる。
You can sense the person's character from the way he speaks.
Logical 'quality' — used in logic/philosophy to denote a specific attribute or property a proposition or object possesses.
哲学の授業で、感覚の質について議論した。
In philosophy class, we discussed the qualities of perception.