I came up with a definition up in post #9:
-Identical containers and hiding styles
-Distance between caches is at or close to the proximity guideline limit of 0.1 miles
-Hiding spots are obvious and easy/quick to access
- >~20 caches
The way I see it, they're called power trails because number-junkies can "power" through them to increase their numbers. Anything that could interfere with this and slow down the hunt, such as varying containers/hiding styles or large distances between, preclude a series from being a "power trail".
I have have to say that a power trail does not necessarily have all the same type containers, nor necessarily be "quick and easy"
I have a power trail here in middle TN, the Team Trunk Monkey Turnpike, (search for TTMT if you want to look it up) And while many of the hides are what I would consider a "traditional power trail hide" with a simple filmcan hidden in a guardrail or at the base of a signpost, I have hidden several small and regular containers in interesting locations, as they made themselves available... just to break up the monotony. There are even a couple of evil little nanos in pretty tough spots, and some magnetic keyholders in unlikely locations... as appropriate to the locale.
I would definitely call it a power trail, but perhaps a bit "above average" for the quality of hides wherever possible, and people have commented on the special ones, and even given some of them favorite points. If the attribute were implemented, I would surely use it for the whole trail... Just to help folks filter it in or out of their search results.