There are 2 types of jealousy. The most correct definiton would be the feeling of being threatened by a rival in a romantic relationship or losing something of value to another person which happens to be yours already. This is what I consider the correct definiton.
The second is type of jealousy is more like Envy. Envy is a hatred/bitterness towards another person for having an advantage that YOU don't have. For instance, envious/jealous behavior such as a friend has a nice new car and instead of being truly happy for them you badmouth them or the car or make up something ridiculous because YOU can't afford it yourself. If someone has money and YOU don't you say they recieved it through less than stellar means. If someone is more talented than YOU you say their work isnt as good as anyone thinks or they are just lucky. This kind of 'jealousy' is destructive and displays itself as having a bad attitude towards the object of the envy and also being passive aggressive.
1. Cher was jealous when her relationship with her boyfriend was threatened.
2. Mike was jealous of her because he didn't have any nice things. He had no happiness so he didnt want her to have any either.