Ransom: Originally, the word 'ransom' referred to money people paid to get someone who was kidnapped back. Online, it means the actor infecting computers and then asking for money in order to allow people to have access to their data again.
The latest example we have we WANNACRY, which demanded money to allow PC users to have their data back.
Revenge porn: this is an act of violation of trust. It is when people end a relationship and the man decides to post intimate photos or videos online to destroy a their ex's reputation, as well as her social and professional life.
Identity theft: It's when a computer is infected with malware (a bad software) that copies passwords and allow criminals to buy things and make bank transactions pretending to be the other person.