Reading some more comments got me thinking.
When someone tells you that he is going to run some 400m intervals, do you know what they mean? My guess is "yes" you know that the person is going to run 400m and then have a period of recovery.
Couldn't both be intervals? The work breaks up the rest and the rest breaks up the work.
I do think having a common terminology can be important when coaches (or athletes) start to discuss training. When a person says he does an LT or tempo run, I ask him to define that. Which LT? (In science there are a dozen or more ways to determine the pace at LT as the science does not refer to a specific pace but that LT is a more general term). I also ask to define tempo. I usually want to know in relation to 10K race pace. I then actually have a better idea of the intensity.
When I was young tempo meant an extended run at a "good" pace. I think over time it is evolved into what I now consider to be a run at a pace just slower than 10K race pace (or maybe half marathon pace--they would be pretty close to one another in a well trained runner).
This is one reason I really like to anchor workout times based on race times. It eliminates a lot of ambiguity.