What is extortion and blackmail?

The term "extortion" gets used a lot but, technically, it has a very specific, common law meaning. In short, common law extortion occurs when someone who is an officer of some public office uses their position of power to receive payment or compensation from their victim. Like if a police officer told you they would not give you a ticket if you gave them $20, or if a park administration officers threatened to cancel your child's birthday party at the public park unless you gave them half of the cake. It's an abuse of power, by person in public office, against someone who is in someway under the authority of that public office.

In contrast, blackmail is a much more modern, broad crime that applies to any person who uses some sort of threat to obtain property from their victim. Note that sometimes it can be difficult to argue whether or not a threat rises to the level of "blackmail" because people threaten other people all the time. If Karen is eating at Applebee's and tells the manager "If you don't give me 50% off my order, I'll never eat here again," this is a threat to try to obtain something of value from Applebee's, but it's not really within the realm of blackmail... Karen is just being jerk. However, if Karen is the president of her local Homeowners Association and tells the manager, "Give me your car, otherwise I'll make sure none of my members ever eat here again," suddenly we creep into the realm of "blackmail."

Note that the immediacy of the threat matters. If Bob tells Sam, "Give me your wallet or I am going punch you," Bob has committed robbery. In contrast, if Bob tells Sam, "Give me your wallet or I am going to tell everyone all of the secrets you told me that would destroy your family," Bob has committed blackmail.