The "stop-and-wait" protocol is a simple method used in data communication. In this approach, a sender transmits a single data packet and then pauses to wait for an acknowledgment from the receiver before sending the next packet. This ensures that the sender knows the packet was received successfully before continuing. This method is straightforward but can be inefficient, especially over long distances or in high-latency networks. If the acknowledgment is delayed, the sender remains idle, which can slow down the overall data transfer rate. Despite its limitations, stop-and-wait is easy to implement and understand.