Why is Clinton famous for using the word is?

Answer 1

To try to avoid perjury he questioned what "is" meant

Answer 2

Clinton is famous for using the word "is" because of his response during the Monica Lewinsky scandal where he famously stated "It depends on what the meaning of the word 'is' is." This response was seen as an attempt to parse words and manipulate the truth, which became a defining moment of his presidency and a source of controversy.