ITIL stands for Information Technology Infrastructure Library. This library is a set of detailed practices for IT service management (ITSM) that focuses on aligning IT with the business needs.

Axelos is the company that has been responsible for the ITIL's further development since 2003.
https://www.axelos.com/best-practice-solutions/itil/what-is-itil

The following five core publications describe the ITIL best practices:

  1. ITIL Service Strategy;
  2. ITIL Service Design;
  3. ITIL Service Transition;
  4. ITIL Service Operation;
  5. ITIL Continual Service Improvement.