What is "deterministic latency"

Can someone please provide a definition of "deterministic latency". For example, I've seen the following quote re OpenSolaris "OpenSolaris must allow for deterministic latency in order to support real-time applications" I've also heard that it's very important for high performance real time networks in domains such as trading.

Can someone explain what it is, why it's important and how you can test a network or communications path to see if it exhibits this property. Thanks.

In context of real time systems by deterministic we mean a guaranteed upper limit on latency under all system conditions. The design should ensure that no matter what upper bound will never be crossed. For testing this a careful analysis of system is must.

It's another way to say "fixed latency." Certain types of computing, particularly when measuring things, require known fixed latencies. That way, you know that measurements were taken as far apart as you received them and if it's a known latency you can be sure exactly when the measurements were taken.

Latency is the amount of time between when a message is sent and when that message is received.

It seems that a guaranteed upper bound on latency is a better concept than fixed latency as fixed implies the latency will always be exactly X, which I don't believe is too likely. Thanks for your feedback. I've seen the term referred to but never defined. All uses of the term made it sound somewhat like a service agreement which is somewhat like a "guaranteed upper bound".