From the way this sentence is expressed I think the writer is suggesting that in his view latency and delay are the same. Otherwise he would have written "... include bandwidth, latency, delay and packet-loss ratio."Thank you, guys.
Here is the original paragraph:
"QoS Metrics — QoS metrics include bandwidth, latency or delay, and packet-loss ratio. Depending on the application, these metrics or their variants could be used for WSNs. For example, sensor nodes may be used to transmit continuous images for target tracking. These nodes generate high-speed data streams and require higher bandwidth than most event-based applications. For a delay-sensitive application, WSNs may also require timely delivery data."
I have searched in Wikipedia, but still can't get the difference.