Is latency equivalent to RTT?

[Michael.Dillon () radianz com]

Has it become common usage to define latency in an IP network as the round 
trip time in that network?

I've always considered latency to be a one-way measure of delay and RTT to 
be the sum of the latencies in both directions. When I tried to find 
something to back up this view, I discovered that a number of companies 
define latency as equivalent to RTT in their SLAs.

Assuming that one has measuring devices in every PoP, do you think it is 
harder to measure a full matrix of one way latency compared to measuring a 
full matrix of RTT? 

Does it even make sense to measure a full matrix of RTT when the 
measurement of A to B to A should be equivalent to the measurement of B to 
A to B?

--Michael Dillon