Difference between Quality and Grade:
Quality is an attribute that describes how well something works. It is often measured by its performance against specifications. In contrast, the grade is a measure of the relative value of different products or services.
What is Quality?
Quality is the degree to which a product or service meets customer expectations at any given time. A quality system focuses on meeting those expectations to maintain or improve customer satisfaction.
The formal definition of quality as per ISO 9000 2015 is:
"Quality: degree to which a set of inherent characteristics of an object fulfils requirements".
What is a Grade?
Think of grade as a category of the product. Different grades of the products have the same functional use but different technical characteristics.
Here is the formal definition of grade according to ISO 9001 2015:
Grade: "category or rank given to different requirements for an object having the same functional use". Example: Class of airline ticket and category of hotel in a hotel brochure.
For example, a $1 Raymond pen and $1000 Montblanc pen are both used to write. As long as both are serving this purpose satisfactorily, both have good quality.
However, the Montblanc pen is a separate category of luxury products. Hence it is a different grade or product.
So next time, when you have to compare the quality of the $1 Raymond pen and $1000 Montblanc pen, don't say that the Montblanc pen is of better quality. It is just a different grade or category. You can not compare apples and oranges.
Also, high grade does not imply high quality.