Since both words indicate a smaller amount, it can be difficult to know when to use the word less or the word fewer in a sentence.
In general, the word ‘fewer’ is used only to describe things that can be counted. You can have fewer people, fewer flower and fewer ingredients.
The word ‘less’ is more often used when talking about singular mass nouns. A singular mass noun is an unclear quantity or intangible quantity such as; less salt, less dreaming, less meaning.
Over the years the meanings and uses of the words less and fewer have changed a few times. This is why we still find some common uses of the words that seem wrong to use. The most popular example is the sign, “10 items or less” at the grocery store.
Technically under today’s rules it should be “10 items or fewer” because you can count the items.