When you say quantity, this means that you are referring to the number of items that are being produced. For example, there are some people who would rather buy in quantity rather than quality because they know that the items will be consumed immediately. For example, there are some cheap pieces of meat because they are not the best grade available.
They will be cooked in order to serve more people. Quality means that the item may not be many in number but it is made with the best items that are available. For example, quality meat usually costs a lot of money but people who have tried it say that you can usually taste and feel the difference.