What is a Windows Azure Compute Hour? [duplicate]
This is the time that your process (Hosted by Azure) is loaded and executing. Your charges are calculated by a combination of Compute Hour and bandwidth used.
I see that someone is trying to close this Question. I think this is a fair question for stackoverflow, it's on the edge of being a programming question (Azure compute is an environment very relevant to programming) and doesn't fit nicely anywhere else.
Just to give a definitive response (I work on the Windows Azure team), Chris Lutz's answer is absolutely correct.