Cooties are the plural term for cooty which means a parasitic louse that infests on human beings. It also means a children's word for a make-believe germ or disgusting quality transmitted by noxious or slovenly people.
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Cooties are parasitic louses that infest the body of human beings.
Cooties refer to diseases that the opposite sex has giving reasons to not be around them. These diseases in late stages are known as 'STDs'. The first known use of this word in English dates back in 1917.