200 and 201 fall under the success family. They indicate that an operation was successful. Plain 200 (Operation Successful) is a successful CRUD Operation:

• 200 (Successful Operation) is the most common type of response status code in REST
• 201 (Successfully Created) is returned when a POST operation successfully creates a resource on the server
• 204 (No content) is issued when a client needs a status but not any data back