We've had customers ask us the same too. There used to be a KB article but I can't find it..
But basically its the total number of connections per hour, rather than unique connections per hour.
Also, its worth noting the LOGPROCESS_MIN_DURATION option that is available, you can use this to set centova to ignore listener sessions less than x seconds, say 5 seconds, as some media players may connect more than once when the listener connects, therefore skewing your stats.
Hopefully one of the centova staff will answer you more specific questions!