This is the 205th most frequent Chinese word.
质量
"质量" means "quality" or "mass" in English, depending on the context.
In this sentence, '质量' refers to the standard of something as measured against other things of a similar kind; it is about the perceived excellence or lack thereof of the product.
这个产品的质量非常好。
The quality of this product is very good.
Here, '质量' is used abstractly to describe the overall excellence or effectiveness of learning.
学习的质量比学习的时间更重要。
The quality of learning is more important than the length of study.
In this context, '质量' is used in a scientific sense to refer to the physical property of mass.