Madame Defarge is a fictional character from Charles Dickens' work A Tale of Two Cities. She is arguably the main villain of the book, and is a tireless worker in the French Revolution. She is a picture of scheming and bitterness.
She's used as a representative of the Greek Fates. The Fates would cut an individual string that represented each person's life. A person could not live longer than the Fates had determined, which was represented by their own string. Madame Defarge would always be knitting, and as she knit, in her mind, she would be knitting the names of those she wanted to die into her work.
In the story, she seeks the lives of Charles Darnay's family out of vengeance for the lives of several of her own family members.
Madame Defarge shows up as a character in Mel Brooks' movie A History Of The World: Part One. Humorously, in his version, she has run out of wool, so she just sits there rubbing her knitting needles together.
Most people who allude to Madame Defarge will be alluding to her scheming nature, and will most likely reference her knitting.