Which word is used incorrectly in the following sentence? She has less books than I do.

The term that appears to be used incorrectly in the sentence "She has less books than I do" is "less." In standard English, "less" is typically used to refer to uncountable nouns, while "fewer" is the correct term for countable nouns. Since "books" is a countable noun (you can count books one by one), "fewer" should be used instead. Therefore, the sentence should read: "She has fewer books than I do." Using "less" in this context suggests a misunderstanding of the distinction between countable and uncountable quantities, highlighting the grammatical principle that countable items require "fewer."