1. What is it?

Jealousy is a feeling of insecurity or fear brought about by the possibility of losing something or someone, particularly to a rival.

Jealousy is different from envy. Envy is wanting what another person has. Jealousy is insecurity about Losing what you have to another.

Jealousy can lead to a person acting bitterly against either the rival, or the person they have in their life.

2. How is it made?

3. Examples in literature

Wives and Concubines 
by Su Tong

Excerpt (translated from Chinese):

Chen Zuoqian’s hand moved from Lotus’s breast to her mouth. “Don’t talk. Don’t talk now.”
Just at that moment someone knocked lightly on the bedroom door. The two of them were startled; Chen Zuoqian looked at Lotus and shook his head, then put out the lamp. In a little while the knocking started again. Chen Zuoqian jumped up and shouted angrily, “Who’s that knocking?”
A timid girlish voice came from the outside the door. “Third Mistress is sick; she’s calling for the Master.”
Chen Zuoqian said, “She’s lying, lying again. Go back and tell her I’ve already gone to bed.”
The girl outside the door said, “The Third Mistress is very sick; she says you have to come. She says she’s about to die.”
Chen Zuoqian sat on the bed and thought for a minute, mumbling to himself, “What’s she up to this time?” Lotus watched his uneasiness, then pushed him. “You’d better go. It would be terrible if she really died.”

Anna Karenina 
by Leo Tolstoy

Excerpt from Part 6, Chapter 32 (translated from Russian):

Before Vronsky’s departure for the elections, Anna had reflected that the scenes constantly repeated between them each time he left home, might only make him cold to her instead of attaching him to her, and resolved to do all she could to control herself so as to bear the parting with composure. But the cold, severe glance with which he had looked at her when he came to tell her he was going had wounded her, and before he had started her peace of mind was destroyed.
In solitude afterwards, thinking over that glance which had expressed his right to freedom, she came, as she always did, to the same point—the sense of her own humiliation. “He has the right to go away when and where he chooses. Not simply to go away, but to leave me. He has every right, and I have none. But knowing that, he ought not to do it. What has he done, though?… He looked at me with a cold, severe expression. Of course that is something indefinable, impalpable, but it has never been so before, and that glance means a great deal,” she thought. “That glance shows the beginning of indifference.”
And though she felt sure that a coldness was beginning, there was nothing she could do, she could not in any way alter her relations to him. Just as before, only by love and by charm could she keep him. And so, just as before, only by occupation in the day, by morphine at night, could she stifle the fearful thought of what would be if he ceased to love her. It is true there was still one means; not to keep him—for that she wanted nothing more than his love—but to be nearer to him, to be in such a position that he would not leave her. That means was divorce and marriage. And she began to long for that, and made up her mind to agree to it the first time he or Stiva approached her on the subject.