What is Tribology?
Tribology is the study of science and engineering of interacting surfaces in relative motion. It includes the study and application of the principles of friction, lubrication and wear. 
Tribology is an interdisciplinary field that includes mechanical engineering materials science and engineering chemistry and chemical engineering and more. This wide variety of skills is necessary because many different physical phenomena occur at a sliding interface. There are also many different areas of focus within tribology. Generally speaking, there are three major topics within tribology: friction, wear and lubrication. 
References:
https://en.wikipedia.org/wiki/Tribology
http://www.stle.org/files/What_is_tribology/Tribology.aspx