What is an ontology?
A body of formally represented knowledge is based on a conceptualization: the objects, concepts, and other entities that are presumed to exist in some area of interest and the relationships that hold them (Genesereth & Nilsson, 1987). A conceptualization is an abstract, simplified view of the world that we wish to represent for some purpose. Every knowledge base, knowledge-based system, or knowledge-level agent is committed to some conceptualization, explicitly or implicitly.
An ontology is an explicit specification of a conceptualization. The term is borrowed from philosophy, where an ontology is a systematic account of Existence. For knowledge-based systems, what “exists” is exactly that which can be represented.
Source: Gruber, T.R. 1993. A Translation Approach to Portable Ontology Specification. Knowledge Acquisition 5: 199-220. http://tomgruber.org/writing/ontolingua-kaj-1993.pdf
Editor’s (Abhay Rautela) notes
The word Ontology comes from two Greek words- ‘Onto’ which means existence and ‘Logia’ which means science.
The semantic web can be considered as a light weight ontology.