The Stop-and-Wait Protocol is a simple method used in data communication where a sender transmits a single packet of data and then waits for an acknowledgment from the receiver before sending the next packet. This ensures that the sender knows the data was received successfully before continuing, reducing the chance of data loss. In this protocol, if the sender does not receive an acknowledgment within a certain time frame, it will resend the packet. This process continues until the sender receives confirmation, making it reliable but potentially slow, especially in networks with high latency or long distances between the sender and receiver.