While looking through the pricing of some cloud computing hosting services like Google App engine, Amazon, etc, I see terms like $0.0x per instance per hour, etc. What exactly does that mean? Is an instance = X page views, or is there any other way to estimate how many instances I would need?
Generally 1 instance == 1 machine/server (often a virtual machine).
See e.g. http://aws.amazon.com/ec2/instance-types/ and https://developers.google.com/appengine/docs/adminconsole/instances