Less and Fewer
We use less to describe the quantity of something. Usually we use less with uncountable nouns.
Sam drinks less coffee than Paul.
Coffee is uncountable; we talk about the quantity or amount of coffee (a cup of coffee, a litre of coffee).
We use fewer to describe the number of items. We use fewer with countable nouns.
Paul eats fewer biscuits than Sam.
Biscuits are countable; we talk about the number of biscuits (2 biscuits, 10 biscuits).
Learn more about countable and uncountable nouns.