ITIL is the 'IT Infrastructure Library'. It was published originally by the UK government (OGC) to provide a disciplined framework for the provision of IT services (both support and delivery).
Since then adoption has certainly snowballed and it is more or less the international standard on these matters.
So what has this got to do with help desk management? Well... everything!
Help desk management (this is actually known as 'service desk management' under ITIL) is a core discipline within the library. It embraces all aspects of help desk management and creates an effective and widely used help desk management framework, splitting the function into two areas: Incident Control and Communication.
As take up of ITIL continues at a rapid pace, and its benefits become clear (consistency, assured quality, etc) it is becoming a far more common currency in help desk circles. It is certainly a factor the forward looking help desk manager cannot ignore.