What does "green-eyed monster" mean?

Jealousy, as in Bella knew that her husband sometimes succumbed to the green-eyed monster. This expression was coined by Shakespeare in Othello (3:3), where Iago says: “O! beware, my lord, of jealousy; it is the green-eyed monster which doth mock the meat it feeds on.” It is thought to allude to cats, often green-eyed, who tease their prey. Also see green with envy.