Just What is an ITIL Service Anyway?
Well yes, and no (of course). Now we will mess it up by exploring a grey area.
Not all customers want to trust IT as a total service provider (for good historical reasons). They are not willing to black box the services, to use the application service provider (ASP) model (now software as a service (SaaS) but still the same model). They are not willing to look only at what comes out of the pipe.
They either (a) want to know about the ponds, pumps, purifications and pipes and define the consumable in those terms or (b) they want to provide some of those themselves. In that case, they are treating IT as an infrastructure service provider (ISP) (and you thought it meant Internet).
The customer wants to take some responsibility for their applications, and looks to IT for platform (servers, operating systems, desktops, databases, network, etc.), storage, bandwidth, and/or management (security, availability, backup and recovery, etc.). This is common in geeky departments like engineering but it can crop up anywhere.
Neither ASP nor ISP is correct. Whether one or the other model is preferred (or prohibited) should be defined in the IT part of the business' strategic plan, and each service definition should make clear where it fits. What is important is for all parties to be clear on what the model is. Confusion and disagreement vanish the moment people realised they are talking on different levels.
If we can ignore that real-world intrusion into the idealised total service provider model we can come up with a slightly more precise definition that still does not become too waffly: An IT service is the availability and/or consumption of a type of transaction running on technology.
Availability and/or consumption? Every service provider sells the services they provide, even internal corporate service providers. There can be services that someone is already consuming, and there can be services that are there but nobody is taking them yet.
There, we cant make it any easier than that.