What's the difference between sending and delivering short messages?

Different states. Sending means that the SMS has been successfully sent to the SMS center of the mobile phone operator, waiting for further sending and delivery. In the sent state, the short message may not reach the receiver's mobile phone; Sent means that the short message has been successfully sent to the receiver's mobile phone, and the receiver's mobile phone has received the short message. In the sent state, the short message has reached the receiver's mobile phone, but it is not sure whether the receiver has read the short message.