Partitive Structure with Uncountable Nouns

To count or quantify an uncountable noun we use a unit of measurement - a measure word. For example, we cannot usually say “two breads” because “bread” is uncountable. So, if we want to specify a quantity of bread we use a measure word such as “loaf” or “slice” in a structure like “two loaves of bread” or “two slices of bread”. We call this structure a partitive structure.

partitive structure: quantity measure word of uncountable noun
examples: two cups of coffee
several games of tennis
a drop of water

We can use the same uncountable noun in different partitive expressions with different meanings. For example, a loaf of bread and a slice of bread are partitive expressions with different meanings. A loaf of bread is what we call a whole unit of bread that we buy from a baker. A slice of bread is what we call a smaller unit of bread after it has been cut from a loaf. 

Here are some more examples:

The word "partitive" indicates that only "part" of a whole is being referred to. The partitive structure using a measure word is common with uncountable nouns, but it can also be used with countable nouns, for example: a series of accidents, two boxes of matches, a can of worms.