This is a common sign we see at supermarkets. "10 items or less"— this is WRONG.
-You use "less" when you are referring to things you are unable to count.
-You use "fewer" when you can count the items individually.
I want a cup of coffee with less sugar in it. (can’t count sugar)
I have fewer assessment books this year because I am lazy. (books can be counted.)
You use "less" to describe time, money or distance.
The speech was less than two hours.
They paid the teacher less than $1,000.