I recently got an offer from Amazon India and I want to know what does 5 RSU mean..Can anyone help?

Education: Btech in Computer Science
Years of Experience : 7months
Offer Date : 26/04/2021
Base:16LPA
1st year Joning Bonus : 5.5LPA
2nd year Joning Bonus : 3LPA
Relocation : 1.5LPA