Define 'network latency'.

Network latency refers to the time taken for data to travel from the source to the destination across a network. This encompasses various delays that can occur during this process, including any processing time at routers and switches, queuing delays due to network congestion, and the propagation delay caused by the physical distance between the communicating devices. High latency can result in slower response times and can significantly affect the performance of applications, especially those requiring real-time communication, such as video calls or online gaming.

In contrast, the other options focus on different aspects of network performance. The speed of data transfer relates to bandwidth, which indicates how much data can be transmitted in a given time frame, rather than the delay experienced during transmission. The amount of data loss over a connection deals with packet loss, a separate issue that indicates whether all the transmitted data successfully reaches the destination. Lastly, the rate of data packet sending and receiving, while important for determining overall network throughput, does not directly measure the time it takes for a single packet to make the journey from point A to point B, which is the essence of network latency.